# source:branches/HeuristicLab.Problems.GrammaticalOptimization/HeuristicLab.Problems.GrammaticalOptimization/ExpressionInterpreter.cs@12024

Last change on this file since 12024 was 12024, checked in by gkronber, 7 years ago

#2283: changed handling of inverse expressions in transformation of expressions to canonical form

File size: 4.4 KB
Line
1using System;
2using System.Collections.Generic;
4using System.Linq;
5using System.Runtime.CompilerServices;
6using System.Runtime.Remoting.Messaging;
7using System.Text;
9using HeuristicLab.Common;
10
11namespace HeuristicLab.Problems.GrammaticalOptimization {
12  public class ExpressionInterpreter {
13    private static readonly double[] emptyErc = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
14
15    private string sentence;
16    private int syIdx;
17    // interprets sentences from L(G(Expr)):
18    // Expr -> Term { ('+' | '-' | '^' ) Term }
19    // Term -> Fact { ('*' | '%') Fact }
20    // Fact -> '!' Expr | '(' Expr ')' | Var | const
21    // Var -> 'a'..'z'
22    // const -> '0' .. '9'
23
24    // uses protected division symbol %
25    // constants are Koza-style ephemeral random constants (ERC). for now we only allow up to 10 constants.
26    // The constant symbols '0' .. '9' are treated as ERC indices
27
28    // for boolean problems the symbol * representes the AND operator, the symbol + represents the OR operator, ! = NOT, ^ = XOR
29
30    public bool Interpret(string sentence, bool[] vars) {
31      return Interpret(sentence, vars, emptyErc);
32    }
33
34    public bool Interpret(string sentence, bool[] vars, double[] erc) {
35      InitLex(sentence);
36      var d = new double[vars.Length];
37      for (int i = 0; i < vars.Length; i++) d[i] = vars[i] ? 1.0 : 0.0;
38      return !DoubleExtensions.IsAlmost(Expr(d, erc), 0);
39    }
40
41    public double Interpret(string sentence, double[] vars) {
42      return Interpret(sentence, vars, emptyErc);
43    }
44
45    public double Interpret(string sentence, double[] vars, double[] erc) {
46      InitLex(sentence);
47      return Expr(vars, erc);
48    }
49
50
51    private void InitLex(string sentence) {
52      this.sentence = sentence;
53      this.syIdx = 0;
54    }
55
56    private char CurSy() {
57      if (syIdx >= sentence.Length) return '\0';
58      return sentence[syIdx];
59    }
60    private void NewSy() {
61      if (syIdx < sentence.Length) syIdx++;
62    }
63
64    // helper for xor
65    private double Not(double x) {
66      return DoubleExtensions.IsAlmost(x, 0) ? 1.0 : 0.0;
67    }
68
69    private double Expr(double[] d, double[] erc) {
70      var r = 0.0;
71      r = Term(d, erc);
72      var curSy = CurSy();
73      while (curSy == '+' || curSy == '-' || curSy == '^') {
74        if (curSy == '+') {
75          NewSy();
76          r += Term(d, erc);
77        } else if (curSy == '-') {
78          NewSy();
79          r -= Term(d, erc);
80        } else {
81          NewSy();
82          var e = Expr(d, erc);
83          r = Not(r) * e + r * Not(e); // xor = (!x AND y) OR (x AND !y)
84        }
85        curSy = CurSy();
86      }
87      return r;
88    }
89
90    private double Term(double[] d, double[] erc) {
91      var r = 0.0;
92      r = Fact(d, erc);
93      var curSy = CurSy();
94      while (curSy == '*' || curSy == '%') {
95        if (curSy == '*') {
96          NewSy();
97          r *= Fact(d, erc);
98        } else {
99          NewSy();
100          var nom = Fact(d, erc);
101          if (HeuristicLab.Common.Extensions.IsAlmost(nom, 0.0)) nom = 1.0;
102          r /= nom;
103        }
104        curSy = CurSy();
105      }
106      return r;
107    }
108
109    private double Fact(double[] d, double[] erc) {
110      double r = 0.0;
111      var curSy = CurSy();
112      if (curSy == '!') {
113        NewSy();
114        r = Not(Expr(d, erc));
115      } else if (curSy == '(') {
116        NewSy();
117        r = Expr(d, erc);
118        if (CurSy() != ')') throw new ArgumentException();
119        NewSy();
120      } else if (curSy >= 'a' && curSy <= 'z') {
121        int o = (byte)curSy - (byte)'a';
122        //int o = Convert.ToByte(CurSy()) - Convert.ToByte('a');
123        if (o < 0 || o >= d.Length) throw new ArgumentException();
124        r = d[o];
125        NewSy();
126      } else if (curSy == '/') {
127        // /-symbol is used in the expressionextender to represent inverse (1/x).
128        // this is necessary because we also use symbols 0..9 as indices for ERCs
129        NewSy();
130        r = 1.0 / Fact(d, erc);
131      } else /* if (curSy >= '0' && curSy <= '9') */ {
132        int o = (byte)curSy - (byte)'0';
133        //int o = Convert.ToByte(CurSy()) - Convert.ToByte('a');
134        if (o < 0 || o >= 10) throw new ArgumentException();
135        r = erc[o];
136        NewSy();
137      }
138      //} else throw new ArgumentException();
139      return r;
140    }
141
142  }
143}
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