source: branches/MCTS-SymbReg-2796/Tests/HeuristicLab.Algorithms.DataAnalysis-3.4/MctsSymbolicRegressionTest.cs @ 15438

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using HeuristicLab.Algorithms.DataAnalysis.MCTSSymbReg;
using HeuristicLab.Data;
using HeuristicLab.Optimization;
using HeuristicLab.Problems.DataAnalysis;
using HeuristicLab.Problems.Instances.DataAnalysis;
using HeuristicLab.Random;
using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace HeuristicLab.Algorithms.DataAnalysis.MctsSymbolicRegression {
  [TestClass()]
  public class MctsSymbolicRegressionTest {
    #region heuristics
    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void TestSimple2dInteractions() {
      {
        // a, b ~ U(0, 1) should be trivial
        var nRand = new MersenneTwister(1234);

        int n = 10000; // large sample so that we can use the thresholds below
        var a = Enumerable.Range(0, n).Select(_ => nRand.NextDouble()).ToArray();
        var b = Enumerable.Range(0, n).Select(_ => nRand.NextDouble()).ToArray();
        var x = Enumerable.Range(0, n).Select(_ => nRand.NextDouble()).ToArray();
        var y = Enumerable.Range(0, n).Select(_ => nRand.NextDouble()).ToArray();

        var z = a.Zip(b, (ai, bi) => ai * bi).ToArray();

        Assert.IsTrue(Heuristics.CorrelationForInteraction(a, b, z) > 0.05); // should be detected as relevant
        Assert.IsTrue(Heuristics.CorrelationForInteraction(a, x, z) > 0.05); // a and b > 0 so these should be detected as well
        Assert.IsTrue(Heuristics.CorrelationForInteraction(a, y, z) > 0.05);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(b, x, z) > 0.05);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(b, y, z) > 0.05);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(x, y, z) < 0.05);
      }
      {
        // a, b ~ U(1000, 2000) also trivial
        var nRand = new UniformDistributedRandom(new MersenneTwister(1234), 1000, 2000);

        int n = 10000; // large sample so that we can use the thresholds below
        var a = Enumerable.Range(0, n).Select(_ => nRand.NextDouble()).ToArray();
        var b = Enumerable.Range(0, n).Select(_ => nRand.NextDouble()).ToArray();
        var x = Enumerable.Range(0, n).Select(_ => nRand.NextDouble()).ToArray();
        var y = Enumerable.Range(0, n).Select(_ => nRand.NextDouble()).ToArray();

        var z = a.Zip(b, (ai, bi) => ai * bi).ToArray();

        Assert.IsTrue(Heuristics.CorrelationForInteraction(a, b, z) > 0.05); // should be detected as relevant
        Assert.IsTrue(Heuristics.CorrelationForInteraction(a, x, z) > 0.05);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(a, y, z) > 0.05);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(b, x, z) > 0.05);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(b, y, z) > 0.05);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(x, y, z) < 0.05);
      }
      {
        // a, b ~ U(-1, 1) 
        var nRand = new UniformDistributedRandom(new MersenneTwister(1234), -1, 1);

        int n = 10000; // large sample so that we can use the thresholds below
        var a = Enumerable.Range(0, n).Select(_ => nRand.NextDouble()).ToArray();
        var b = Enumerable.Range(0, n).Select(_ => nRand.NextDouble()).ToArray();
        var x = Enumerable.Range(0, n).Select(_ => nRand.NextDouble()).ToArray();
        var y = Enumerable.Range(0, n).Select(_ => nRand.NextDouble()).ToArray();

        var z = a.Zip(b, (ai, bi) => ai * bi).ToArray();

        Assert.IsTrue(Heuristics.CorrelationForInteraction(a, b, z) > 0.05); // should be detected as relevant
        Assert.IsTrue(Heuristics.CorrelationForInteraction(a, x, z) < 0.05);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(a, y, z) < 0.05);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(b, x, z) < 0.05);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(b, y, z) < 0.05);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(x, y, z) < 0.05);
      }
      {
        // a, b ~ N(0, 1)
        var nRand = new NormalDistributedRandom(new MersenneTwister(1234), 0, 1);

        int n = 10000; // large sample so that we can use the thresholds below
        var a = Enumerable.Range(0, n).Select(_ => nRand.NextDouble()).ToArray();
        var b = Enumerable.Range(0, n).Select(_ => nRand.NextDouble()).ToArray();
        var x = Enumerable.Range(0, n).Select(_ => nRand.NextDouble()).ToArray();
        var y = Enumerable.Range(0, n).Select(_ => nRand.NextDouble()).ToArray();

        var z = a.Zip(b, (ai, bi) => ai * bi).ToArray();

        Assert.IsTrue(Heuristics.CorrelationForInteraction(a, b, z) > 0.05); // should be detected as relevant
        Assert.IsTrue(Heuristics.CorrelationForInteraction(a, x, z) < 0.05);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(a, y, z) < 0.05);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(b, x, z) < 0.05);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(b, y, z) < 0.05);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(x, y, z) < 0.05);
      }
      {
        var rand = new MersenneTwister(1234);
        // a ~ N(100, 1), b ~ N(-100, 1)
        var nRand = new NormalDistributedRandom(rand, 0, 1);
        var aRand = new NormalDistributedRandom(rand, 100, 1);
        var bRand = new NormalDistributedRandom(rand, -100, 1);

        int n = 10000; // large sample so that we can use the thresholds below
        var a = Enumerable.Range(0, n).Select(_ => aRand.NextDouble()).ToArray();
        var b = Enumerable.Range(0, n).Select(_ => bRand.NextDouble()).ToArray();
        var x = Enumerable.Range(0, n).Select(_ => nRand.NextDouble()).ToArray();
        var y = Enumerable.Range(0, n).Select(_ => nRand.NextDouble()).ToArray();

        var z = a.Zip(b, (ai, bi) => ai * bi).ToArray();

        Assert.IsTrue(Heuristics.CorrelationForInteraction(a, b, z) > 0.05); // should be detected as relevant
        Assert.IsTrue(Heuristics.CorrelationForInteraction(a, x, z) > 0.05); // a > 0
        Assert.IsTrue(Heuristics.CorrelationForInteraction(a, y, z) > 0.05);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(b, x, z) > 0.05); // b < 0
        Assert.IsTrue(Heuristics.CorrelationForInteraction(b, y, z) > 0.05);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(x, y, z) < 0.05); // random variables are not correlated
      }
    }

    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void TestGeneral2dInteractions() {
      {
        // we should be able to reliably detect when a product of two variables is correlated with the target variable        

        // the test samples x from a two dimensional normal distribution
        // the covariance matrix for the normal distribution is randomly sampled 
        // this means x_1 and x_2 might be highly correlated
        // the mean of the normal distribution is randomly sampled (most critical are probably zero-mean distributions)
        // y is calculated as x_1*x_2

        var conditionNumber = 10000;
        for (int iter = 0; iter < 100; iter++) {
          double m0 = 0.0; double m1 = 0.0;
          alglib.hqrndstate randState;
          alglib.hqrndseed(1234, 31415, out randState);

          // uncomment if non-zero mean distributions should be tested
          //alglib.hqrndnormal2(randState, out m0, out m1);

          double[,] cov_ab = new double[2, 2];
          double[,] cov_xy = new double[2, 2];
          alglib.matgen.spdmatrixrndcond(2, conditionNumber, ref cov_ab);
          alglib.spdmatrixcholesky(ref cov_ab, 2, true);

          alglib.matgen.spdmatrixrndcond(2, conditionNumber, ref cov_xy);
          alglib.spdmatrixcholesky(ref cov_xy, 2, true);

          // generate a, b by sampling from a 2dim multivariate normal distribution
          // generate x, y by sampling from another 2dim multivariate normal distribution
          // a,b and x,y might be correlated but x,y are not correlated to a,b
          int N = 1000; // large sample size to make sure the test thresholds hold
          double[] a = new double[N];
          double[] b = new double[N];
          double[] x = new double[N];
          double[] y = new double[N];
          double[] z = new double[N];

          for (int i = 0; i < N; i++) {
            double r1, r2, r3, r4;
            alglib.hqrndnormal2(randState, out r1, out r2);
            alglib.hqrndnormal2(randState, out r3, out r4);

            var r_ab = new double[] { r1, r2 };
            var r_xy = new double[] { r3, r4 };
            double[] s_ab = new double[2];
            double[] s_xy = new double[2];
            alglib.ablas.rmatrixmv(2, 2, cov_ab, 0, 0, 0, r_ab, 0, ref s_ab, 0);
            alglib.ablas.rmatrixmv(2, 2, cov_xy, 0, 0, 0, r_xy, 0, ref s_xy, 0);

            a[i] = s_ab[0] + m0;
            b[i] = s_ab[1] + m1;
            x[i] = s_xy[0] + m0; // use same mean (just for the sake of it)
            y[i] = s_xy[1] + m1;

            z[i] = a[i] * b[i];
          }

          Assert.IsTrue(Heuristics.CorrelationForInteraction(a, b, z) > 0.05);
          Assert.IsTrue(Heuristics.CorrelationForInteraction(x, y, z) < 0.05);

          /* we might see correlations when only using one of the two relevant factors.
           * this depends on the distribution / location of a and b 
          // for zero-mean distributions the following should all be quasi-zero
          Assert.IsTrue(Heuristics.CorrelationForInteraction(a, x, z) < 0.05);
          Assert.IsTrue(Heuristics.CorrelationForInteraction(b, x, z) < 0.05);
          Assert.IsTrue(Heuristics.CorrelationForInteraction(a, y, z) < 0.05);
          Assert.IsTrue(Heuristics.CorrelationForInteraction(b, y, z) < 0.05);
          */
          Console.WriteLine("a,b: {0:N3}\tx,y: {1:N3}\ta,x: {2:N3}\tb,x: {3:N3}\ta,y: {4:N3}\tb,y: {5:N3}\tcov(a,b): {6:N3}",
            Heuristics.CorrelationForInteraction(a, b, z),
            Heuristics.CorrelationForInteraction(x, y, z),
            Heuristics.CorrelationForInteraction(a, x, z),
            Heuristics.CorrelationForInteraction(b, x, z),
            Heuristics.CorrelationForInteraction(a, y, z),
            Heuristics.CorrelationForInteraction(b, y, z),
            alglib.cov2(a, b)
            );
        }
      }
    }
    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void TestGeneral3dInteractions() {
      {
        // same as TestGeneral2dInteractions but for terms with three variables

        var conditionNumber = 100;
        for (int iter = 0; iter < 100; iter++) {
          double m0 = 0.0; double m1 = 0.0; double m2 = 0.0;
          alglib.hqrndstate randState;
          alglib.hqrndseed(1234, 31415, out randState);

          // uncomment if non-zero mean distributions should be tested
          //alglib.hqrndnormal2(randState, out m0, out m1);
          //alglib.hqrndnormal2(randState, out m1, out m2);

          double[,] cov_abc = new double[3, 3];
          double[,] cov_xyz = new double[3, 3];
          alglib.matgen.spdmatrixrndcond(3, conditionNumber, ref cov_abc);
          alglib.spdmatrixcholesky(ref cov_abc, 3, true);

          alglib.matgen.spdmatrixrndcond(3, conditionNumber, ref cov_xyz);
          alglib.spdmatrixcholesky(ref cov_xyz, 3, true);

          int N = 1000; // large sample size to make sure the test thresholds hold
          double[] a = new double[N];
          double[] b = new double[N];
          double[] c = new double[N];
          double[] x = new double[N];
          double[] y = new double[N];
          double[] z = new double[N];
          double[] t = new double[N];

          for (int i = 0; i < N; i++) {
            double r1, r2, r3, r4, r5, r6;
            alglib.hqrndnormal2(randState, out r1, out r2);
            alglib.hqrndnormal2(randState, out r3, out r4);
            alglib.hqrndnormal2(randState, out r5, out r6);

            var r_abc = new double[] { r1, r2, r3 };
            var r_xyz = new double[] { r4, r5, r6 };
            double[] s_abc = new double[3];
            double[] s_xyz = new double[3];
            alglib.ablas.rmatrixmv(3, 3, cov_abc, 0, 0, 0, r_abc, 0, ref s_abc, 0);
            alglib.ablas.rmatrixmv(3, 3, cov_xyz, 0, 0, 0, r_xyz, 0, ref s_xyz, 0);

            a[i] = s_abc[0] + m0;
            b[i] = s_abc[1] + m1;
            c[i] = s_abc[2] + m2;
            x[i] = s_xyz[0] + m0; // use same mean (just for the sake of it)
            y[i] = s_xyz[1] + m1;
            z[i] = s_xyz[2] + m2;

            t[i] = a[i] * b[i] * c[i];
          }

          Assert.IsTrue(Heuristics.CorrelationForInteraction(a, b, c, t) > 0.05);
          Assert.IsTrue(Heuristics.CorrelationForInteraction(x, y, z, t) < 0.05);

          /* we might see correlations when only using one of the two relevant factors.
           * this depends on the distribution / location of a and b 
          // for zero-mean distributions the following should all be quasi-zero
          Assert.IsTrue(Heuristics.CorrelationForInteraction(a, x, z) < 0.05);
          Assert.IsTrue(Heuristics.CorrelationForInteraction(b, x, z) < 0.05);
          Assert.IsTrue(Heuristics.CorrelationForInteraction(a, y, z) < 0.05);
          Assert.IsTrue(Heuristics.CorrelationForInteraction(b, y, z) < 0.05);
          */
          Console.WriteLine("a,b,c: {0:N3}\tx,y,z: {1:N3}\ta,b,x: {2:N3}\tb,c,x: {3:N3}",
            Heuristics.CorrelationForInteraction(a, b, c, t),
            Heuristics.CorrelationForInteraction(x, y, z, t),
            Heuristics.CorrelationForInteraction(a, b, x, t),
            Heuristics.CorrelationForInteraction(b, c, x, t)
            );
        }
      }
    }

    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void TestPoly10Interactions() {
      {
        alglib.hqrndstate randState;
        alglib.hqrndseed(1234, 31415, out randState);

        int N = 25000; // large sample size to make sure the test thresholds hold
        double[] a = new double[N];
        double[] b = new double[N];
        double[] c = new double[N];
        double[] d = new double[N];
        double[] e = new double[N];
        double[] f = new double[N];
        double[] g = new double[N];
        double[] h = new double[N];
        double[] i = new double[N];
        double[] j = new double[N];
        double[] y = new double[N];

        for(int k=0;k<N;k++) {
          a[k] = alglib.hqrnduniformr(randState) * 2 - 1;
          b[k] = alglib.hqrnduniformr(randState) * 2 - 1;
          c[k] = alglib.hqrnduniformr(randState) * 2 - 1;
          d[k] = alglib.hqrnduniformr(randState) * 2 - 1;
          e[k] = alglib.hqrnduniformr(randState) * 2 - 1;
          f[k] = alglib.hqrnduniformr(randState) * 2 - 1;
          g[k] = alglib.hqrnduniformr(randState) * 2 - 1;
          h[k] = alglib.hqrnduniformr(randState) * 2 - 1;
          i[k] = alglib.hqrnduniformr(randState) * 2 - 1;
          j[k] = alglib.hqrnduniformr(randState) * 2 - 1;
          y[k] = a[k] * b[k] + c[k] * d[k] + e[k] * f[k] + a[k] * g[k] * i[k] + c[k] * f[k] * j[k];
        }

        var x = new[] { a, b, c, d, e, f, g, h, i, j };
        var all2Combinations = HeuristicLab.Common.EnumerableExtensions.Combinations(new[] {1,2,3,4,5,6,7,8,9,10}, 2);

        var resultList = new List<Tuple<string, double>>();
        foreach(var entry in all2Combinations) {
          var aIdx = entry.First();
          var bIdx = entry.Skip(1).First();
          resultList.Add(Tuple.Create(aIdx + " " + bIdx, Heuristics.CorrelationForInteraction(x[aIdx - 1], x[bIdx - 1], y)));
        }

        foreach(var entry in resultList.OrderByDescending(t => t.Item2)) {
          Console.WriteLine("{0} {1:N3}", entry.Item1, entry.Item2);
        }

        var all3Combinations = HeuristicLab.Common.EnumerableExtensions.Combinations(new[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 }, 3);

        resultList = new List<Tuple<string, double>>();
        foreach (var entry in all3Combinations) {
          var aIdx = entry.First();
          var bIdx = entry.Skip(1).First();
          var cIdx = entry.Skip(2).First();
          resultList.Add(Tuple.Create(aIdx + " " + bIdx + " " + cIdx, Heuristics.CorrelationForInteraction(x[aIdx - 1], x[bIdx - 1], x[cIdx - 1], y)));
        }

        //  Y = X1*X2 + X3*X4 + X5*X6 + X1*X7*X9 + X3*X6*X10

        foreach (var entry in resultList.OrderByDescending(t => t.Item2)) {
          Console.WriteLine("{0} {1:N3}", entry.Item1, entry.Item2);
        }


        Assert.IsTrue(Heuristics.CorrelationForInteraction(a, b, y) > 0.01);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(b, a, y) > 0.01);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(c, d, y) > 0.01);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(d, c, y) > 0.01);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(e, f, y) > 0.01);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(f, e, y) > 0.01);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(a, g, i, y) > 0.01);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(a, i, g, y) > 0.01);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(g, a, i, y) > 0.01);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(g, i, a, y) > 0.01);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(i, g, a, y) > 0.01);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(i, a, g, y) > 0.01);

        Assert.IsTrue(Heuristics.CorrelationForInteraction(c, f, j, y) > 0.01);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(c, j, f, y) > 0.01);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(f, c, j, y) > 0.01);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(f, j, c, y) > 0.01);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(j, c, f, y) > 0.01);
        Assert.IsTrue(Heuristics.CorrelationForInteraction(j, f, c, y) > 0.01);
      }
    }
    #endregion


    #region expression hashing
    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void ExprHashTest() {
      int nParams;
      byte[] code;

      {
        // addition of variables
        var codeGen = new CodeGenerator();
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 1);
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 2);
        codeGen.Emit1(OpCodes.Add);
        codeGen.Emit1(OpCodes.Exit);
        codeGen.GetCode(out code, out nParams);
        var h1 = ExprHash.GetHash(code, nParams);

        codeGen = new CodeGenerator();
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 2);
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 1);
        codeGen.Emit1(OpCodes.Add);
        codeGen.Emit1(OpCodes.Exit);
        codeGen.GetCode(out code, out nParams);
        var h2 = ExprHash.GetHash(code, nParams);

        Assert.AreEqual(h1, h2);
      }

      {
        // multiplication of variables
        var codeGen = new CodeGenerator();
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 1);
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 2);
        codeGen.Emit1(OpCodes.Mul);
        codeGen.Emit1(OpCodes.Exit);
        codeGen.GetCode(out code, out nParams);
        var h1 = ExprHash.GetHash(code, nParams);

        codeGen = new CodeGenerator();
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 2);
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 1);
        codeGen.Emit1(OpCodes.Mul);
        codeGen.Emit1(OpCodes.Exit);
        codeGen.GetCode(out code, out nParams);
        var h2 = ExprHash.GetHash(code, nParams);

        Assert.AreEqual(h1, h2);
      }

      {
        // distributivity 
        var codeGen = new CodeGenerator();
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 1);
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 2);
        codeGen.Emit1(OpCodes.Add);
        codeGen.Emit2(OpCodes.LoadVar, 3);
        codeGen.Emit1(OpCodes.Mul);
        codeGen.Emit1(OpCodes.Exit);
        codeGen.GetCode(out code, out nParams);
        var h1 = ExprHash.GetHash(code, nParams);

        codeGen = new CodeGenerator();
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 2);
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 3);
        codeGen.Emit1(OpCodes.Mul);
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 1);
        codeGen.Emit2(OpCodes.LoadVar, 3);
        codeGen.Emit1(OpCodes.Mul);
        codeGen.Emit1(OpCodes.Add);
        codeGen.Emit1(OpCodes.Exit);
        codeGen.GetCode(out code, out nParams);
        var h2 = ExprHash.GetHash(code, nParams);

        Assert.AreEqual(h1, h2);
      }


      {
        // div 
        var codeGen = new CodeGenerator();
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 1);
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 2);
        codeGen.Emit1(MctsSymbolicRegression.OpCodes.Mul);
        codeGen.Emit1(OpCodes.Inv);
        codeGen.Emit1(OpCodes.Exit);
        codeGen.GetCode(out code, out nParams);
        var h1 = ExprHash.GetHash(code, nParams);

        codeGen = new CodeGenerator();
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 1);
        codeGen.Emit1(OpCodes.Inv);
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 2);
        codeGen.Emit1(OpCodes.Inv);
        codeGen.Emit1(MctsSymbolicRegression.OpCodes.Mul);
        codeGen.Emit1(OpCodes.Exit);
        codeGen.GetCode(out code, out nParams);
        var h2 = ExprHash.GetHash(code, nParams);

        Assert.AreEqual(h1, h2);
      }
      {
        // exp
        var codeGen = new CodeGenerator();
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 1);
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 2);
        codeGen.Emit1(MctsSymbolicRegression.OpCodes.Add);
        codeGen.Emit1(OpCodes.Exp);
        codeGen.Emit1(OpCodes.Exit);
        codeGen.GetCode(out code, out nParams);
        var h1 = ExprHash.GetHash(code, nParams);

        codeGen = new CodeGenerator();
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 1);
        codeGen.Emit1(OpCodes.Exp);
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 2);
        codeGen.Emit1(OpCodes.Exp);
        codeGen.Emit1(MctsSymbolicRegression.OpCodes.Mul);
        codeGen.GetCode(out code, out nParams);
        codeGen.Emit1(OpCodes.Exit);
        var h2 = ExprHash.GetHash(code, nParams);

        Assert.AreEqual(h1, h2);
      }
      {
        // log
        var codeGen = new CodeGenerator();
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 1);
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 2);
        codeGen.Emit1(MctsSymbolicRegression.OpCodes.Mul);
        codeGen.Emit1(OpCodes.Log);
        codeGen.Emit1(OpCodes.Exit);
        codeGen.GetCode(out code, out nParams);
        var h1 = ExprHash.GetHash(code, nParams);

        codeGen = new CodeGenerator();
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 1);
        codeGen.Emit1(OpCodes.Log);
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 2);
        codeGen.Emit1(OpCodes.Log);
        codeGen.Emit1(MctsSymbolicRegression.OpCodes.Add);
        codeGen.Emit1(OpCodes.Exit);
        codeGen.GetCode(out code, out nParams);
        var h2 = ExprHash.GetHash(code, nParams);

        Assert.AreEqual(h1, h2);
      }

      {
        // x1 + x1 is equivalent to x1
        var codeGen = new CodeGenerator();
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 1);
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 1);
        codeGen.Emit1(OpCodes.Add);
        codeGen.Emit1(OpCodes.Exit);
        codeGen.GetCode(out code, out nParams);
        var h1 = ExprHash.GetHash(code, nParams);

        codeGen = new CodeGenerator();
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 1);
        codeGen.Emit1(OpCodes.Exit);
        codeGen.GetCode(out code, out nParams);
        var h2 = ExprHash.GetHash(code, nParams);

        Assert.AreEqual(h1, h2);
      }
      {
        // c1*x1 + c2*x1 is equivalent to c3*x1
        var codeGen = new CodeGenerator();
        codeGen.Emit1(MctsSymbolicRegression.OpCodes.LoadParamN);
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 1);
        codeGen.Emit1(MctsSymbolicRegression.OpCodes.Mul);

        codeGen.Emit1(MctsSymbolicRegression.OpCodes.LoadParamN);
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 1);
        codeGen.Emit1(MctsSymbolicRegression.OpCodes.Mul);

        codeGen.Emit1(OpCodes.Add);
        codeGen.Emit1(OpCodes.Exit);
        codeGen.GetCode(out code, out nParams);
        var h1 = ExprHash.GetHash(code, nParams);

        codeGen = new CodeGenerator();
        codeGen.Emit1(MctsSymbolicRegression.OpCodes.LoadParamN);
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 1);
        codeGen.Emit1(MctsSymbolicRegression.OpCodes.Mul);
        codeGen.Emit1(OpCodes.Exit);
        codeGen.GetCode(out code, out nParams);
        var h2 = ExprHash.GetHash(code, nParams);

        Assert.AreEqual(h1, h2);
      }

      {
        var codeGen = new CodeGenerator();
        codeGen.Emit1(MctsSymbolicRegression.OpCodes.LoadConst0);
        codeGen.Emit1(MctsSymbolicRegression.OpCodes.LoadConst1);
        codeGen.Emit1(MctsSymbolicRegression.OpCodes.LoadParamN);
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 1);
        codeGen.Emit1(MctsSymbolicRegression.OpCodes.Mul);

        codeGen.Emit1(MctsSymbolicRegression.OpCodes.LoadParamN);
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 1);
        codeGen.Emit1(MctsSymbolicRegression.OpCodes.Mul);

        codeGen.Emit1(OpCodes.Add);

        codeGen.Emit1(MctsSymbolicRegression.OpCodes.Mul);
        codeGen.Emit1(MctsSymbolicRegression.OpCodes.Add);

        codeGen.Emit1(OpCodes.Exit);
        codeGen.GetCode(out code, out nParams);
        var h1 = ExprHash.GetHash(code, nParams);

        codeGen = new CodeGenerator();
        codeGen.Emit1(MctsSymbolicRegression.OpCodes.LoadConst0);
        codeGen.Emit1(MctsSymbolicRegression.OpCodes.LoadConst1);
        codeGen.Emit1(MctsSymbolicRegression.OpCodes.LoadParamN);
        codeGen.Emit2(MctsSymbolicRegression.OpCodes.LoadVar, 1);
        codeGen.Emit1(MctsSymbolicRegression.OpCodes.Mul);
        codeGen.Emit1(MctsSymbolicRegression.OpCodes.Mul);
        codeGen.Emit1(MctsSymbolicRegression.OpCodes.Add);
        codeGen.Emit1(OpCodes.Exit);
        codeGen.GetCode(out code, out nParams);
        var h2 = ExprHash.GetHash(code, nParams);

        Assert.AreEqual(h1, h2);
      }
    }
    #endregion

    #region number of solutions
    // the algorithm should visits each solution only once
    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void MctsSymbRegNumberOfSolutionsOneVariable() {
      // this problem has only one variable
      var provider = new NguyenInstanceProvider();
      var regProblem = provider.LoadData(provider.GetDataDescriptors().Single(x => x.Name.Contains("F1 ")));
      {
        // possible solutions with max one variable reference:
        // x
        // log(x)
        // exp(x)
        // 1/x
        TestMctsNumberOfSolutions(regProblem, 1, 4);
      }
      {
        // possible solutions with max 4 variable references:
        // without exp, log and inv
        // x       
        // x*x
        // x*x*x
        // x+x*x
        // x+x*x*x
        // x*x*x*x

        TestMctsNumberOfSolutions(regProblem, 4, 6, allowLog: false, allowInv: false, allowExp: false);
      }
      {
        // possible solutions with max 5 variable references:
        // without exp, log and inv
        // x       
        // xx
        // xxx
        // x+xx
        // xxxx
        // x+xxx
        // xxxxx 
        // x+xxxx
        // xx+xxx
        TestMctsNumberOfSolutions(regProblem, 5, 9, allowLog: false, allowInv: false, allowExp: false);
      }
      {
        // possible solutions with max two variable references:
        // x
        // log(x+c)
        // exp(x)
        // 1/(x+c)
        //              -- 4
        // x * x
        // x * log(x+c)
        // x * exp(x)
        // x * 1/(x + c)
        // x + log(x+c)
        // x + exp(x)
        // x + 1/(x+c)
        //              -- 7
        // log(x + c) * log(x + c)
        // log(x + c) * exp(x)
        // log(x + c) * 1/(x + c)
        // log(x + c) + log(x + c)                        // TODO
        // log(x + c) + exp(x)
        // log(x + c) + 1/(x+c)
        //              -- 6
        // exp(x) * 1/(x+c)
        // exp(cx) + exp(cx)                              // TODO
        // exp(cx) + 1/(x+c)
        //              -- 3
        // 1/(x+c) * 1/(x+c)                              // TODO
        // 1/(x+c) + 1/(x+c)                              // TODO
        //              -- 2
        // log(x*x)
        // exp(x*x)
        // inv(x*x+c)
        //              -- 3


        TestMctsNumberOfSolutions(regProblem, 2, 27);
      }
      {
        // possible solutions with max three variable references:
        // without log and inv
        // x
        // exp(x)
        //              -- 2
        // x * x
        // x + x                                            ?
        // x * exp(x)
        // x + exp(x)
        // exp(x) * exp(x)
        // exp(x) + exp(x)                                  ?
        // exp(x*x)
        //              -- 7
        // x * x * x
        // x + x * x                                       
        // x + x + x                                        ?
        // x * x * exp(x)
        // x + x * exp(x)                                   
        // x + x + exp(x)                                   ?
        // exp(x) + x*x
        // exp(x) + x*exp(x)                                
        // x + exp(x) * exp(x)                              
        // x + exp(x) + exp(x)                              ?
        // x * exp(x) * exp(x)
        // x * exp(x*x)
        // x + exp(x*x)
        //              -- 13

        // exp(x) * exp(x) * exp(x)
        // exp(x) + exp(x) * exp(x)                         
        // exp(x) + exp(x) + exp(x)                         ?
        //              -- 3

        // exp(x)   * exp(x*x)
        // exp(x)   + exp(x*x)
        //              -- 2
        // exp(x*x*x)
        //              -- 1
        TestMctsNumberOfSolutions(regProblem, 3, 2 + 7 + 13 + 3 + 2 + 1, allowLog: false, allowInv: false);
      }      
    }

    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void MctsSymbRegNumberOfSolutionsTwoVariables() {
      // this problem has only two input variables
      var provider = new HeuristicLab.Problems.Instances.DataAnalysis.NguyenInstanceProvider();
      var regProblem = provider.LoadData(provider.GetDataDescriptors().Single(x => x.Name.Contains("F9 ")));
      {
        // possible solutions with max one variable reference:
        // x
        // log(x)
        // exp(x)
        // 1/x
        // y
        // log(y)
        // exp(y)
        // 1/y
        TestMctsNumberOfSolutions(regProblem, 1, 8);
      }
      {
        // possible solutions with max one variable reference:
        // without log and inv

        // x
        // exp(x)
        // y
        // exp(y)
        TestMctsNumberOfSolutions(regProblem, 1, 4, allowLog: false, allowInv: false);
      }
      {
        // possible solutions with max two variable references:
        // without log and inv

        // x
        // y
        // exp(x)
        // exp(y)
        //                  -- 4
        // x (*|+) x
        // x (*|+) exp(x)
        // x (*|+) y
        // x (*|+) exp(y)
        //                  -- 8
        // exp(x) (*|+) exp(x)
        // exp(x) (*|+) exp(y)
        //                  -- 4
        // y (*|+) y
        // y (*|+) exp(x)
        // y (*|+) exp(y)
        //                  -- 6
        // exp(y) (*|+) exp(y)
        //                  -- 2
        //
        // exp(x*x)
        // exp(x*y)
        // exp(y*y)
        //                  -- 3

        TestMctsNumberOfSolutions(regProblem, 2, 4 + 8 + 4 + 6 + 2 + 3, allowLog: false, allowInv: false);
      }

      {
        // possible solutions with max two variable references:
        // without exp and sum
        // x
        // y
        // log(x)
        // log(y)
        // inv(x)
        // inv(y)
        //              -- 6
        // x * x
        // x * y
        // x * log(x)
        // x * log(y)
        // x * inv(x)
        // x * inv(y)
        //              -- 6
        // log(x) * log(x)
        // log(x) * log(y)
        // log(x) * inv(x)
        // log(x) * inv(y)
        //              -- 4
        // inv(x) * inv(x)
        // inv(x) * inv(y)
        //              -- 2
        // y * y
        // y * log(x)
        // y * log(y)
        // y * inv(x)
        // y * inv(y)
        //              -- 5
        // log(y) * log(y)
        // log(y) * inv(x)
        // log(y) * inv(y)
        //              -- 3
        // inv(y) * inv(y)
        //              -- 1
        // log(x*x)
        // log(x*y)
        // log(y*y)

        // inv(x*x)
        // inv(x*y)
        // inv(y*y)
        //             -- 6
        // log(x+x)
        // log(x+y)
        // log(y+y)

        // inv(x+x)
        // inv(x+y)
        // inv(y+y)
        //             -- 6
        TestMctsNumberOfSolutions(regProblem, 2, 6 + 6 + 4 + 2 + 5 + 3 + 1 + 6 + 6, allowExp: false, allowSum: false);
      }
    }
    #endregion


    #region test structure search (no constants)
    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void MctsSymbReg_NoConstants_Nguyen1() {
      // x³ + x² + x
      var provider = new HeuristicLab.Problems.Instances.DataAnalysis.NguyenInstanceProvider(seed: 1234);
      var regProblem = provider.LoadData(provider.GetDataDescriptors().Single(x => x.Name.Contains("F1 ")));
      TestMctsWithoutConstants(regProblem, nVarRefs: 10, allowExp: false, allowLog: false, allowInv: false);
    }
    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void MctsSymbReg_NoConstants_Nguyen2() {
      // x^4 + x³ + x² + x
      var provider = new HeuristicLab.Problems.Instances.DataAnalysis.NguyenInstanceProvider(seed: 1234);
      var regProblem = provider.LoadData(provider.GetDataDescriptors().Single(x => x.Name.Contains("F2 ")));
      TestMctsWithoutConstants(regProblem, allowExp: false, allowLog: false, allowInv: false);
    }
    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void MctsSymbReg_NoConstants_Nguyen3() {
      // x^5 + x^4 + x³ + x² + x
      var provider = new HeuristicLab.Problems.Instances.DataAnalysis.NguyenInstanceProvider(seed: 1234);
      var regProblem = provider.LoadData(provider.GetDataDescriptors().Single(x => x.Name.Contains("F3 ")));
      TestMctsWithoutConstants(regProblem, nVarRefs: 15, iterations: 1000000, allowExp: false, allowLog: false, allowInv: false);
    }
    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void MctsSymbReg_NoConstants_Nguyen4() {
      // x^6 + x^5 + x^4 + x³ + x² + x
      var provider = new HeuristicLab.Problems.Instances.DataAnalysis.NguyenInstanceProvider(seed: 1234);
      var regProblem = provider.LoadData(provider.GetDataDescriptors().Single(x => x.Name.Contains("F4 ")));
      TestMctsWithoutConstants(regProblem, nVarRefs: 25, iterations: 1000000, allowExp: false, allowLog: false, allowInv: false);
    }

    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void MctsSymbReg_NoConstants_Nguyen7() {
      // log(x + 1) + log(x² + 1)
      var provider = new HeuristicLab.Problems.Instances.DataAnalysis.NguyenInstanceProvider(seed: 1234);
      var regProblem = provider.LoadData(provider.GetDataDescriptors().Single(x => x.Name.Contains("F7 ")));
      TestMctsWithoutConstants(regProblem, nVarRefs: 10, iterations: 100000, allowExp: false, allowLog: true, allowInv: false);
    }

    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void MctsSymbReg_NoConstants_Poly10_Part1() {
      var provider = new HeuristicLab.Problems.Instances.DataAnalysis.VariousInstanceProvider(seed: 1234);
      var regProblem = provider.LoadData(provider.GetDataDescriptors().Single(x => x.Name.Contains("Poly-10")));

      //  Y = X1*X2 + X3*X4 + X5*X6 + X1*X7*X9 + X3*X6*X10
      //  Y' = X1*X2 + X3*X4 + X5*X6
      // simplify problem by changing target
      var ds = ((Dataset)regProblem.Dataset).ToModifiable();
      var ys = ds.GetDoubleValues("Y").ToArray();
      var x1 = ds.GetDoubleValues("X1").ToArray();
      var x2 = ds.GetDoubleValues("X2").ToArray();
      var x3 = ds.GetDoubleValues("X3").ToArray();
      var x4 = ds.GetDoubleValues("X4").ToArray();
      var x5 = ds.GetDoubleValues("X5").ToArray();
      var x6 = ds.GetDoubleValues("X6").ToArray();
      var x7 = ds.GetDoubleValues("X7").ToArray();
      var x8 = ds.GetDoubleValues("X8").ToArray();
      var x9 = ds.GetDoubleValues("X9").ToArray();
      var x10 = ds.GetDoubleValues("X10").ToArray();
      for (int i = 0; i < ys.Length; i++) {
        ys[i] -= x1[i] * x7[i] * x9[i];
        ys[i] -= x3[i] * x6[i] * x10[i];
      }
      ds.ReplaceVariable("Y", ys.ToList());

      var modifiedProblemData = new RegressionProblemData(ds, regProblem.AllowedInputVariables, regProblem.TargetVariable);


      TestMctsWithoutConstants(modifiedProblemData, nVarRefs: 15, iterations: 100000, allowExp: false, allowLog: false, allowInv: false);
    }

    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void MctsSymbReg_NoConstants_Poly10_Part2() {
      var provider = new HeuristicLab.Problems.Instances.DataAnalysis.VariousInstanceProvider(seed: 1234);
      var regProblem = provider.LoadData(provider.GetDataDescriptors().Single(x => x.Name.Contains("Poly-10")));

      //  Y = X1*X2 + X3*X4 + X5*X6 + X1*X7*X9 + X3*X6*X10
      //  Y' = X1*X7*X9 + X3*X6*X10
      // simplify problem by changing target
      var ds = ((Dataset)regProblem.Dataset).ToModifiable();
      var ys = ds.GetDoubleValues("Y").ToArray();
      var x1 = ds.GetDoubleValues("X1").ToArray();
      var x2 = ds.GetDoubleValues("X2").ToArray();
      var x3 = ds.GetDoubleValues("X3").ToArray();
      var x4 = ds.GetDoubleValues("X4").ToArray();
      var x5 = ds.GetDoubleValues("X5").ToArray();
      var x6 = ds.GetDoubleValues("X6").ToArray();
      var x7 = ds.GetDoubleValues("X7").ToArray();
      var x8 = ds.GetDoubleValues("X8").ToArray();
      var x9 = ds.GetDoubleValues("X9").ToArray();
      var x10 = ds.GetDoubleValues("X10").ToArray();
      for (int i = 0; i < ys.Length; i++) {
        ys[i] -= x1[i] * x2[i];
        ys[i] -= x3[i] * x4[i];
        ys[i] -= x5[i] * x6[i];
      }
      ds.ReplaceVariable("Y", ys.ToList());

      var modifiedProblemData = new RegressionProblemData(ds, regProblem.AllowedInputVariables, regProblem.TargetVariable);


      TestMctsWithoutConstants(modifiedProblemData, nVarRefs: 15, iterations: 100000, allowExp: false, allowLog: false, allowInv: false);
    }

    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void MctsSymbReg_NoConstants_Poly10_Part3() {
      var provider = new HeuristicLab.Problems.Instances.DataAnalysis.VariousInstanceProvider(seed: 1234);
      var regProblem = provider.LoadData(provider.GetDataDescriptors().Single(x => x.Name.Contains("Poly-10")));

      //  Y = X1*X2 + X3*X4 + X5*X6 + X1*X7*X9 + X3*X6*X10
      //  Y' = X1*X2 + X1*X7*X9
      // simplify problem by changing target
      var ds = ((Dataset)regProblem.Dataset).ToModifiable();
      var ys = ds.GetDoubleValues("Y").ToArray();
      var x1 = ds.GetDoubleValues("X1").ToArray();
      var x2 = ds.GetDoubleValues("X2").ToArray();
      var x3 = ds.GetDoubleValues("X3").ToArray();
      var x4 = ds.GetDoubleValues("X4").ToArray();
      var x5 = ds.GetDoubleValues("X5").ToArray();
      var x6 = ds.GetDoubleValues("X6").ToArray();
      var x7 = ds.GetDoubleValues("X7").ToArray();
      var x8 = ds.GetDoubleValues("X8").ToArray();
      var x9 = ds.GetDoubleValues("X9").ToArray();
      var x10 = ds.GetDoubleValues("X10").ToArray();
      for (int i = 0; i < ys.Length; i++) {
        ys[i] -= x3[i] * x4[i];
        ys[i] -= x5[i] * x6[i];
        ys[i] -= x3[i] * x6[i] * x10[i];
      }
      ds.ReplaceVariable("Y", ys.ToList());

      var modifiedProblemData = new RegressionProblemData(ds, regProblem.AllowedInputVariables, regProblem.TargetVariable);


      TestMctsWithoutConstants(modifiedProblemData, nVarRefs: 15, iterations: 100000, allowExp: false, allowLog: false, allowInv: false);
    }

    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void MctsSymbReg_NoConstants_Poly10_Part4() {
      var provider = new HeuristicLab.Problems.Instances.DataAnalysis.VariousInstanceProvider(seed: 1234);
      var regProblem = provider.LoadData(provider.GetDataDescriptors().Single(x => x.Name.Contains("Poly-10")));

      //  Y = X1*X2 + X3*X4 + X5*X6 + X1*X7*X9 + X3*X6*X10
      //  Y' = X3*X4 + X5*X6 + X3*X6*X10
      // simplify problem by changing target
      var ds = ((Dataset)regProblem.Dataset).ToModifiable();
      var ys = ds.GetDoubleValues("Y").ToArray();
      var x1 = ds.GetDoubleValues("X1").ToArray();
      var x2 = ds.GetDoubleValues("X2").ToArray();
      var x3 = ds.GetDoubleValues("X3").ToArray();
      var x4 = ds.GetDoubleValues("X4").ToArray();
      var x5 = ds.GetDoubleValues("X5").ToArray();
      var x6 = ds.GetDoubleValues("X6").ToArray();
      var x7 = ds.GetDoubleValues("X7").ToArray();
      var x8 = ds.GetDoubleValues("X8").ToArray();
      var x9 = ds.GetDoubleValues("X9").ToArray();
      var x10 = ds.GetDoubleValues("X10").ToArray();
      for (int i = 0; i < ys.Length; i++) {
        ys[i] -= x1[i] * x2[i];
        ys[i] -= x1[i] * x7[i] * x9[i];
      }
      ds.ReplaceVariable("Y", ys.ToList());
      var modifiedProblemData = new RegressionProblemData(ds, regProblem.AllowedInputVariables, regProblem.TargetVariable);


      TestMctsWithoutConstants(modifiedProblemData, nVarRefs: 15, iterations: 100000, allowExp: false, allowLog: false, allowInv: false);
    }

    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void MctsSymbReg_NoConstants_Poly10_Part5() {
      var provider = new HeuristicLab.Problems.Instances.DataAnalysis.VariousInstanceProvider(seed: 1234);
      var regProblem = provider.LoadData(provider.GetDataDescriptors().Single(x => x.Name.Contains("Poly-10")));

      //  Y = X1*X2 + X3*X4 + X5*X6 + X1*X7*X9 + X3*X6*X10
      //  Y' = X1*X2 + X3*X4 + X5*X6 + X1*X7*X9
      // simplify problem by changing target
      var ds = ((Dataset)regProblem.Dataset).ToModifiable();
      var ys = ds.GetDoubleValues("Y").ToArray();
      var x1 = ds.GetDoubleValues("X1").ToArray();
      var x2 = ds.GetDoubleValues("X2").ToArray();
      var x3 = ds.GetDoubleValues("X3").ToArray();
      var x4 = ds.GetDoubleValues("X4").ToArray();
      var x5 = ds.GetDoubleValues("X5").ToArray();
      var x6 = ds.GetDoubleValues("X6").ToArray();
      var x7 = ds.GetDoubleValues("X7").ToArray();
      var x8 = ds.GetDoubleValues("X8").ToArray();
      var x9 = ds.GetDoubleValues("X9").ToArray();
      var x10 = ds.GetDoubleValues("X10").ToArray();
      for (int i = 0; i < ys.Length; i++) {
        ys[i] -= x3[i] * x6[i] * x10[i];
      }
      ds.ReplaceVariable("Y", ys.ToList());
      var modifiedProblemData = new RegressionProblemData(ds, regProblem.AllowedInputVariables, regProblem.TargetVariable);


      TestMctsWithoutConstants(modifiedProblemData, nVarRefs: 15, iterations: 100000, allowExp: false, allowLog: false, allowInv: false);
    }

    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void MctsSymbReg_NoConstants_Poly10_Part6() {
      var provider = new HeuristicLab.Problems.Instances.DataAnalysis.VariousInstanceProvider(seed: 1234);
      var regProblem = provider.LoadData(provider.GetDataDescriptors().Single(x => x.Name.Contains("Poly-10")));

      //  Y = X1*X2 + X3*X4 + X5*X6 + X1*X7*X9 + X3*X6*X10
      //  Y' = X1*X2 + X3*X4 + X5*X6 + X3*X6*X10
      // simplify problem by changing target
      var ds = ((Dataset)regProblem.Dataset).ToModifiable();
      var ys = ds.GetDoubleValues("Y").ToArray();
      var x1 = ds.GetDoubleValues("X1").ToArray();
      var x2 = ds.GetDoubleValues("X2").ToArray();
      var x3 = ds.GetDoubleValues("X3").ToArray();
      var x4 = ds.GetDoubleValues("X4").ToArray();
      var x5 = ds.GetDoubleValues("X5").ToArray();
      var x6 = ds.GetDoubleValues("X6").ToArray();
      var x7 = ds.GetDoubleValues("X7").ToArray();
      var x8 = ds.GetDoubleValues("X8").ToArray();
      var x9 = ds.GetDoubleValues("X9").ToArray();
      var x10 = ds.GetDoubleValues("X10").ToArray();
      for (int i = 0; i < ys.Length; i++) {
        ys[i] -= x1[i] * x7[i] * x9[i];
      }
      ds.ReplaceVariable("Y", ys.ToList());
      var modifiedProblemData = new RegressionProblemData(ds, regProblem.AllowedInputVariables, regProblem.TargetVariable);


      TestMctsWithoutConstants(modifiedProblemData, nVarRefs: 9, iterations: 100000, allowExp: false, allowLog: false, allowInv: false);
    }


    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "long")]
    public void MctsSymbReg_NoConstants_Poly10_250rows() {
      var provider = new HeuristicLab.Problems.Instances.DataAnalysis.VariousInstanceProvider(seed: 1234);
      var regProblem = provider.LoadData(provider.GetDataDescriptors().Single(x => x.Name.Contains("Poly-10")));
      regProblem.TrainingPartition.Start = 0;
      regProblem.TrainingPartition.End = regProblem.Dataset.Rows;
      regProblem.TestPartition.Start = 0;
      regProblem.TestPartition.End = 2;
      TestMctsWithoutConstants(regProblem, nVarRefs: 15, iterations: 200000, allowExp: false, allowLog: false, allowInv: false);
    }
    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "long")]
    public void MctsSymbReg_NoConstants_Poly10_10000rows() {
      // as poly-10 but more rows
      var rand = new FastRandom(1234);
      var x1 = Enumerable.Range(0, 10000).Select(_ => rand.NextDouble()).ToList();
      var x2 = Enumerable.Range(0, 10000).Select(_ => rand.NextDouble()).ToList();
      var x3 = Enumerable.Range(0, 10000).Select(_ => rand.NextDouble()).ToList();
      var x4 = Enumerable.Range(0, 10000).Select(_ => rand.NextDouble()).ToList();
      var x5 = Enumerable.Range(0, 10000).Select(_ => rand.NextDouble()).ToList();
      var x6 = Enumerable.Range(0, 10000).Select(_ => rand.NextDouble()).ToList();
      var x7 = Enumerable.Range(0, 10000).Select(_ => rand.NextDouble()).ToList();
      var x8 = Enumerable.Range(0, 10000).Select(_ => rand.NextDouble()).ToList();
      var x9 = Enumerable.Range(0, 10000).Select(_ => rand.NextDouble()).ToList();
      var x10 = Enumerable.Range(0, 10000).Select(_ => rand.NextDouble()).ToList();
      var ys = new List<double>();
      for (int i = 0; i < x1.Count; i++) {
        ys.Add(x1[i] * x2[i] + x3[i] * x4[i] + x5[i] * x6[i] + x1[i] * x7[i] * x9[i] + x3[i] * x6[i] * x10[i]);
      }

      var ds = new Dataset(new string[] { "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "y" },
        new[] { x1, x2, x3, x4, x5, x6, x7, x8, x9, x10, ys });


      var problemData = new RegressionProblemData(ds, new string[] { "a", "b", "c", "d", "e", "f", "g", "h", "i", "j" }, "y");

      problemData.TrainingPartition.Start = 0;
      problemData.TrainingPartition.End = problemData.Dataset.Rows;
      problemData.TestPartition.Start = 0;
      problemData.TestPartition.End = 2; // must not be empty


      TestMctsWithoutConstants(problemData, nVarRefs: 15, iterations: 100000, allowExp: false, allowLog: false, allowInv: false);
    }

    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void MctsSymbReg_NoConstants_TwoVars() {

      // y = x1 + x2 + x1*x2 + x1*x2*x2 + x1*x1*x2
      var rand = new FastRandom(1234);
      var x1 = Enumerable.Range(0, 100).Select(_ => rand.NextDouble()).ToList();
      var x2 = Enumerable.Range(0, 100).Select(_ => rand.NextDouble()).ToList();
      var ys = x1.Zip(x2, (x1i, x2i) => x1i + x2i + x1i * x2i + x1i * x2i * x2i + x1i * x1i * x2i).ToList();

      var ds = new Dataset(new string[] { "a", "b", "y" }, new[] { x1, x2, ys });

      var problemData = new RegressionProblemData(ds, new string[] { "a", "b" }, "y");


      TestMctsWithoutConstants(problemData, nVarRefs: 10, iterations: 10000, allowExp: false, allowLog: false, allowInv: false);
    }

    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void MctsSymbReg_NoConstants_Misleading() {

      // y = a + baaaaa (the effect of the second term should be very small)
      // the alg will quickly find that a has big effect and will search below a
      // since we prevent a + a... the algorithm must find the correct expression via a + b...
      // however b has a small effect so the branch might not be identified as relevant

      var rand = new FastRandom(1234);
      var @as = Enumerable.Range(0, 100).Select(_ => rand.NextDouble()).ToList();
      var bs = Enumerable.Range(0, 100).Select(_ => rand.NextDouble()).ToList();
      var cs = Enumerable.Range(0, 100).Select(_ => rand.NextDouble() * 1.0e-3).ToList();
      var ds = Enumerable.Range(0, 100).Select(_ => rand.NextDouble()).ToList();
      var es = Enumerable.Range(0, 100).Select(_ => rand.NextDouble()).ToList();
      var ys = new double[@as.Count];
      for (int i = 0; i < ys.Length; i++)
        ys[i] = @as[i] + bs[i] + @as[i] * bs[i] * cs[i];

      var dataset = new Dataset(new string[] { "a", "b", "c", "d", "e", "y" }, new[] { @as, bs, cs, ds, es, ys.ToList() });

      var problemData = new RegressionProblemData(dataset, new string[] { "a", "b", "c", "d", "e" }, "y");


      TestMctsWithoutConstants(problemData, nVarRefs: 10, iterations: 10000, allowExp: false, allowLog: false, allowInv: false);
    }
    #endregion

    #region restricted structure but including numeric constants

    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void MctsSymbRegKeijzer7() {
      // ln(x)
      var provider = new HeuristicLab.Problems.Instances.DataAnalysis.KeijzerInstanceProvider(seed: 1234);
      var regProblem = provider.LoadData(provider.GetDataDescriptors().Single(x => x.Name.Contains("Keijzer 7 f(")));
      // some Keijzer problem instances have very large test partitions (here we are not concerened about test performance)
      if (regProblem.TestPartition.End - regProblem.TestPartition.Start > 1000) regProblem.TestPartition.End = regProblem.TestPartition.Start + 1000;
      TestMcts(regProblem, allowExp: false, allowLog: true, allowInv: false);
    }

    /*
    // [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void MctsSymbRegBenchmarkNguyen5() {
      // sin(x²)cos(x) - 1
      var provider = new HeuristicLab.Problems.Instances.DataAnalysis.NguyenInstanceProvider();
      var regProblem = provider.LoadData(provider.GetDataDescriptors().Single(x => x.Name.Contains("F5 ")));
      TestMcts(regProblem);
    }
    // [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void MctsSymbRegBenchmarkNguyen6() {
      // sin(x) + sin(x + x²)
      var provider = new HeuristicLab.Problems.Instances.DataAnalysis.NguyenInstanceProvider();
      var regProblem = provider.LoadData(provider.GetDataDescriptors().Single(x => x.Name.Contains("F6 ")));
      TestMcts(regProblem);
    }
    */
    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void MctsSymbRegBenchmarkNguyen7() {
      //  log(x + 1) + log(x² + 1)
      var provider = new HeuristicLab.Problems.Instances.DataAnalysis.NguyenInstanceProvider(seed: 1234);
      var regProblem = provider.LoadData(provider.GetDataDescriptors().Single(x => x.Name.Contains("F7 ")));
      TestMcts(regProblem, maxVariableReferences: 5, allowExp: false, allowLog: true, allowInv: false);
    }
    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void MctsSymbRegBenchmarkNguyen8() {
      // Sqrt(x)
      // = x ^ 0.5
      // = exp(0.5 * log(x))
      var provider = new HeuristicLab.Problems.Instances.DataAnalysis.NguyenInstanceProvider(seed: 1234);
      var regProblem = provider.LoadData(provider.GetDataDescriptors().Single(x => x.Name.Contains("F8 ")));
      TestMcts(regProblem, maxVariableReferences: 5, allowExp: true, allowLog: true, allowInv: false);
    }
    /*
    // [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void MctsSymbRegBenchmarkNguyen9() {
      //  sin(x) + sin(y²)
      var provider = new HeuristicLab.Problems.Instances.DataAnalysis.NguyenInstanceProvider();
      var regProblem = provider.LoadData(provider.GetDataDescriptors().Single(x => x.Name.Contains("F9 ")));
      TestMcts(regProblem);
    }
    // [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void MctsSymbRegBenchmarkNguyen10() {
      // 2sin(x)cos(y)
      var provider = new HeuristicLab.Problems.Instances.DataAnalysis.NguyenInstanceProvider();
      var regProblem = provider.LoadData(provider.GetDataDescriptors().Single(x => x.Name.Contains("F10 ")));
      TestMcts(regProblem);
    }
    */
    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void MctsSymbRegBenchmarkNguyen11() {
      // x ^ y  , x > 0, y > 0   
      // = exp(y * log(x))
      var provider = new HeuristicLab.Problems.Instances.DataAnalysis.NguyenInstanceProvider(seed: 1234);
      var regProblem = provider.LoadData(provider.GetDataDescriptors().Single(x => x.Name.Contains("F11 ")));
      TestMcts(regProblem, maxVariableReferences: 5, allowExp: true, allowLog: true, allowInv: false);
    }
    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void MctsSymbRegBenchmarkNguyen12() {
      // x^4 - x³ + y²/2 - y
      var provider = new HeuristicLab.Problems.Instances.DataAnalysis.NguyenInstanceProvider(seed: 1234);
      var regProblem = provider.LoadData(provider.GetDataDescriptors().Single(x => x.Name.Contains("F12 ")));
      TestMcts(regProblem, maxVariableReferences: 20, allowExp: false, allowLog: false, allowInv: false);
    }

    #endregion

    #region keijzer
    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "long")]
    public void MctsSymbRegBenchmarkKeijzer5() {
      // (30 * x * z) / ((x - 10)  * y²)
      // = 30 x z / (xy² - y²)
      var provider = new HeuristicLab.Problems.Instances.DataAnalysis.KeijzerInstanceProvider(seed: 1234);
      var regProblem = provider.LoadData(provider.GetDataDescriptors().Single(x => x.Name.Contains("Keijzer 5 f(")));
      // some Keijzer problem instances have very large test partitions (here we are not concerened about test performance)
      if (regProblem.TestPartition.End - regProblem.TestPartition.Start > 1000) regProblem.TestPartition.End = regProblem.TestPartition.Start + 1000;
      TestMcts(regProblem, maxVariableReferences: 20, allowExp: false, allowLog: false, allowInv: true);
    }

    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void MctsSymbRegBenchmarkKeijzer6() {
      // Keijzer 6 f(x) = Sum(1 / i) From 1 to X  , x \in [0..120]
      // we can only approximate this
      var provider = new HeuristicLab.Problems.Instances.DataAnalysis.KeijzerInstanceProvider(seed: 1234);
      var regProblem = provider.LoadData(provider.GetDataDescriptors().Single(x => x.Name.Contains("Keijzer 6 f(")));
      // some Keijzer problem instances have very large test partitions (here we are not concerened about test performance)
      if (regProblem.TestPartition.End - regProblem.TestPartition.Start > 1000) regProblem.TestPartition.End = regProblem.TestPartition.Start + 1000;
      TestMcts(regProblem, maxVariableReferences: 20, allowExp: false, allowLog: false, allowInv: true);
    }


    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void MctsSymbRegBenchmarkKeijzer8() {
      // sqrt(x)
      var provider = new HeuristicLab.Problems.Instances.DataAnalysis.KeijzerInstanceProvider(seed: 1234);
      var regProblem = provider.LoadData(provider.GetDataDescriptors().Single(x => x.Name.Contains("Keijzer 8 f(")));
      // some Keijzer problem instances have very large test partitions (here we are not concerened about test performance)
      if (regProblem.TestPartition.End - regProblem.TestPartition.Start > 1000) regProblem.TestPartition.End = regProblem.TestPartition.Start + 1000;
      TestMcts(regProblem, maxVariableReferences: 5, allowExp: true, allowLog: true, allowInv: false);
    }

    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void MctsSymbRegBenchmarkKeijzer9() {
      // arcsinh(x)  i.e. ln(x + sqrt(x² + 1))
      var provider = new HeuristicLab.Problems.Instances.DataAnalysis.KeijzerInstanceProvider(seed: 1234);
      var regProblem = provider.LoadData(provider.GetDataDescriptors().Single(x => x.Name.Contains("Keijzer 9 f(")));
      // some Keijzer problem instances have very large test partitions (here we are not concerened about test performance)
      if (regProblem.TestPartition.End - regProblem.TestPartition.Start > 1000) regProblem.TestPartition.End = regProblem.TestPartition.Start + 1000;
      TestMcts(regProblem, maxVariableReferences: 5, allowExp: true, allowLog: true, allowInv: false);
    }

    /* 
    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void MctsSymbRegBenchmarkKeijzer11() {
      // xy + sin( (x-1) (y-1) )
      var provider = new HeuristicLab.Problems.Instances.DataAnalysis.KeijzerInstanceProvider();
      var regProblem = provider.LoadData(provider.GetDataDescriptors().Single(x => x.Name.Contains("Keijzer 11 f(")));
      // some Keijzer problem instances have very large test partitions (here we are not concerened about test performance)
      if (regProblem.TestPartition.End - regProblem.TestPartition.Start > 1000) regProblem.TestPartition.End = regProblem.TestPartition.Start + 1000;
      TestMcts(regProblem, successThreshold: 0.99); // cannot solve this yet
    }
     */
    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void MctsSymbRegBenchmarkKeijzer12() {
      // x^4 - x³ + y² / 2 - y,  same as Nguyen 12             
      var provider = new HeuristicLab.Problems.Instances.DataAnalysis.KeijzerInstanceProvider(seed: 1234);
      var regProblem = provider.LoadData(provider.GetDataDescriptors().Single(x => x.Name.Contains("Keijzer 12 f(")));
      // some Keijzer problem instances have very large test partitions (here we are not concerened about test performance)
      if (regProblem.TestPartition.End - regProblem.TestPartition.Start > 1000) regProblem.TestPartition.End = regProblem.TestPartition.Start + 1000;
      TestMcts(regProblem, maxVariableReferences: 15, allowExp: false, allowLog: false, allowInv: false);
    }
    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void MctsSymbRegBenchmarkKeijzer14() {
      // 8 / (2 + x² + y²)
      var provider = new HeuristicLab.Problems.Instances.DataAnalysis.KeijzerInstanceProvider(seed: 1234);
      var regProblem = provider.LoadData(provider.GetDataDescriptors().Single(x => x.Name.Contains("Keijzer 14 f(")));
      // some Keijzer problem instances have very large test partitions (here we are not concerened about test performance)
      if (regProblem.TestPartition.End - regProblem.TestPartition.Start > 1000) regProblem.TestPartition.End = regProblem.TestPartition.Start + 1000;
      TestMcts(regProblem, maxVariableReferences: 10, allowExp: false, allowLog: false, allowInv: true);
    }
    [TestMethod]
    [TestCategory("Algorithms.DataAnalysis")]
    [TestProperty("Time", "short")]
    public void MctsSymbRegBenchmarkKeijzer15() {
      // x³ / 5 + y³ / 2 - y - x
      var provider = new HeuristicLab.Problems.Instances.DataAnalysis.KeijzerInstanceProvider(seed: 1234);
      var regProblem = provider.LoadData(provider.GetDataDescriptors().Single(x => x.Name.Contains("Keijzer 15 f(")));
      // some Keijzer problem instances have very large test partitions (here we are not concerened about test performance)
      if (regProblem.TestPartition.End - regProblem.TestPartition.Start > 1000) regProblem.TestPartition.End = regProblem.TestPartition.Start + 1000;
      TestMcts(regProblem, maxVariableReferences: 10, allowExp: false, allowLog: false, allowInv: false);
    }
    #endregion

    private void TestMcts(IRegressionProblemData problemData,
      int iterations = 20000,
      double successThreshold = 0.99999,
      int maxVariableReferences = 5,
      bool allowExp = true,
      bool allowLog = true,
      bool allowInv = true,
      bool allowSum = true
      ) {
      var mctsSymbReg = new MctsSymbolicRegressionAlgorithm();
      var regProblem = new RegressionProblem();
      regProblem.ProblemDataParameter.Value = problemData;
      #region Algorithm Configuration
      mctsSymbReg.Problem = regProblem;
      mctsSymbReg.Iterations = iterations;
      mctsSymbReg.MaxVariableReferences = maxVariableReferences;

      mctsSymbReg.SetSeedRandomly = false;
      mctsSymbReg.Seed = 1234;
      mctsSymbReg.AllowedFactors.SetItemCheckedState(mctsSymbReg.AllowedFactors.Single(s => s.Value.Contains("exp")), allowExp);
      mctsSymbReg.AllowedFactors.SetItemCheckedState(mctsSymbReg.AllowedFactors.Single(s => s.Value.Contains("log")), allowLog);
      mctsSymbReg.AllowedFactors.SetItemCheckedState(mctsSymbReg.AllowedFactors.Single(s => s.Value.Contains("1 /")), allowInv);
      mctsSymbReg.AllowedFactors.SetItemCheckedState(mctsSymbReg.AllowedFactors.Single(s => s.Value.Contains("t1(x) + t2(x) + ... ")), allowSum);

      mctsSymbReg.ScaleVariables = true;
      mctsSymbReg.ConstantOptimizationIterations = 0;

      #endregion
      RunAlgorithm(mctsSymbReg);

      Console.WriteLine(mctsSymbReg.ExecutionTime);
      var eps = 1.0 - successThreshold;
      Assert.AreEqual(1.0, ((DoubleValue)mctsSymbReg.Results["Best solution quality (train)"].Value).Value, eps);
      Assert.AreEqual(1.0, ((DoubleValue)mctsSymbReg.Results["Best solution quality (test)"].Value).Value, eps);
    }


    private void TestMctsWithoutConstants(IRegressionProblemData problemData,
      int nVarRefs = 10,
      int iterations = 200000, double successThreshold = 0.99999,
      bool allowExp = true,
      bool allowLog = true,
      bool allowInv = true,
      bool allowSum = true
      ) {
      var mctsSymbReg = new MctsSymbolicRegressionAlgorithm();
      var regProblem = new RegressionProblem();
      regProblem.ProblemDataParameter.Value = problemData;
      #region Algorithm Configuration
      mctsSymbReg.Problem = regProblem;
      mctsSymbReg.Iterations = iterations;
      mctsSymbReg.MaxVariableReferences = nVarRefs;
      mctsSymbReg.SetSeedRandomly = false;
      mctsSymbReg.Seed = 1234;
      mctsSymbReg.AllowedFactors.SetItemCheckedState(mctsSymbReg.AllowedFactors.Single(s => s.Value.Contains("exp")), allowExp);
      mctsSymbReg.AllowedFactors.SetItemCheckedState(mctsSymbReg.AllowedFactors.Single(s => s.Value.Contains("log")), allowLog);
      mctsSymbReg.AllowedFactors.SetItemCheckedState(mctsSymbReg.AllowedFactors.Single(s => s.Value.Contains("1 /")), allowInv);
      mctsSymbReg.AllowedFactors.SetItemCheckedState(mctsSymbReg.AllowedFactors.Single(s => s.Value.Contains("t1(x) + t2(x) + ... ")), allowSum);

      // no constants
      mctsSymbReg.ScaleVariables = false;
      mctsSymbReg.ConstantOptimizationIterations = -1;


      #endregion
      RunAlgorithm(mctsSymbReg);

      Console.WriteLine(mctsSymbReg.ExecutionTime);
      var eps = 1.0 - successThreshold;
      Assert.AreEqual(1.0, ((DoubleValue)mctsSymbReg.Results["Best solution quality (train)"].Value).Value, eps);
      Assert.AreEqual(1.0, ((DoubleValue)mctsSymbReg.Results["Best solution quality (test)"].Value).Value, eps);
    }

    private void TestMctsNumberOfSolutions(IRegressionProblemData problemData, int maxNumberOfVariables, int expectedNumberOfSolutions,
      bool allowProd = true,
      bool allowExp = true,
      bool allowLog = true,
      bool allowInv = true,
      bool allowSum = true
  ) {
      var mctsSymbReg = new MctsSymbolicRegressionAlgorithm();
      var regProblem = new RegressionProblem();
      regProblem.ProblemDataParameter.Value = problemData;
      #region Algorithm Configuration

      mctsSymbReg.SetSeedRandomly = false;
      mctsSymbReg.Seed = 1234;
      mctsSymbReg.Problem = regProblem;
      mctsSymbReg.Iterations = int.MaxValue; // stopping when all solutions have been enumerated
      mctsSymbReg.MaxVariableReferences = maxNumberOfVariables;
      mctsSymbReg.AllowedFactors.SetItemCheckedState(mctsSymbReg.AllowedFactors.Single(s => s.Value.StartsWith("x * y * ...")), allowProd);
      mctsSymbReg.AllowedFactors.SetItemCheckedState(mctsSymbReg.AllowedFactors.Single(s => s.Value.Contains("exp(c * x * y ...)")), allowExp);
      mctsSymbReg.AllowedFactors.SetItemCheckedState(mctsSymbReg.AllowedFactors.Single(s => s.Value.Contains("log(c + c1 x + c2 x + ...)")), allowLog);
      mctsSymbReg.AllowedFactors.SetItemCheckedState(mctsSymbReg.AllowedFactors.Single(s => s.Value.Contains("1 / (1 + c1 x + c2 x + ...)")), allowInv);
      mctsSymbReg.AllowedFactors.SetItemCheckedState(mctsSymbReg.AllowedFactors.Single(s => s.Value.Contains("t1(x) + t2(x) + ... ")), allowSum);
      #endregion
      RunAlgorithm(mctsSymbReg);

      Console.WriteLine(mctsSymbReg.ExecutionTime);
      Assert.AreEqual(expectedNumberOfSolutions, ((IntValue)mctsSymbReg.Results["Iterations"].Value).Value);
    }


    // same as in SamplesUtil
    private void RunAlgorithm(IAlgorithm a) {
      var trigger = new EventWaitHandle(false, EventResetMode.ManualReset);
      Exception ex = null;
      a.Stopped += (src, e) => { trigger.Set(); };
      a.ExceptionOccurred += (src, e) => { ex = e.Value; trigger.Set(); };
      a.Prepare();
      a.Start();
      trigger.WaitOne();

      Assert.AreEqual(ex, null);
    }

  }
}