Changeset 17820

Timestamp:

01/08/21 15:56:42 (4 years ago)

Author:

mkommend

Message:

#2985: changed behavior of root simplification (rootSymbol(a,0) => double.NaN) and added comments for performed simplifications.

Location:

trunk

Files:

• HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Converters/TreeSimplifier.cs (modified) (3 diffs)
• HeuristicLab.Tests/HeuristicLab.Problems.DataAnalysis.Symbolic-3.4/SymbolicDataAnalysisExpressionTreeSimplifierTest.cs (modified) (1 diff)

trunk/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Converters/TreeSimplifier.cs

@@ -934 +934 @@
         var constBValue = Math.Round(constB.Value);
         if (constBValue == 1.0) {
+          // root(a, 1) => a
           return a;
         } else if (constBValue == 0.0) {
-          return MakeConstant(1.0);
+          // root(a, 0) is not defined 
+          //return MakeConstant(1.0);
+          return MakeConstant(double.NaN);
         } else if (constBValue == -1.0) {
+          // root(a, -1) => a^(-1/1) => 1/a
           return MakeFraction(MakeConstant(1.0), a);
         } else if (constBValue < 0) {
+          // root(a, -b) => a^(-1/b) => (1/a)^(1/b) => root(1, b) / root(a, b) => 1 / root(a, b)
           var rootNode = rootSymbol.CreateTreeNode();
           rootNode.AddSubtree(a);
@@ -988 +993 @@
         double exponent = Math.Round(constB.Value);
         if (exponent == 0.0) {
+          // a^0 => 1
           return MakeConstant(1.0);
         } else if (exponent == 1.0) {
+          // a^1 => a
           return a;
         } else if (exponent == -1.0) {
+          // a^-1 => 1/a
           return MakeFraction(MakeConstant(1.0), a);
         } else if (exponent < 0) {
+          // a^-b => (1/a)^b => 1/(a^b)
           var powNode = powSymbol.CreateTreeNode();
           powNode.AddSubtree(a);
@@ -1019 +1028 @@
         return MakeConstant(((ConstantTreeNode)a).Value / ((ConstantTreeNode)b).Value);
       } else if ((IsConstant(a) && ((ConstantTreeNode)a).Value != 1.0)) {
+        // a / x => (a * 1/a) / (x * 1/a) => 1 / (x * 1/a)
         return MakeFraction(MakeConstant(1.0), MakeProduct(b, Invert(a)));
       } else if (IsVariableBase(a) && IsConstant(b)) {

trunk/HeuristicLab.Tests/HeuristicLab.Problems.DataAnalysis.Symbolic-3.4/SymbolicDataAnalysisExpressionTreeSimplifierTest.cs

@@ -99 +99 @@
       #region root rules
       // cancellation
-      AssertEqualAfterSimplification("(root (variable 2.0 a) 0.0)", "1.0");
+      AssertEqualAfterSimplification("(root (variable 2.0 a) 0.0)", "NaN");
       // fixed point
       AssertEqualAfterSimplification("(root (variable 2.0 a) 1.0)", "(variable 2.0 a)");