/// <summary>
/// Checks whether this program is equal to another.
/// </summary>
/// <param name="other">The other program to check for equality.</param>
/// <returns>
/// <c>true</c> if the objects are the same or have the same <see cref="Label" /> and their <see cref="Input" />
/// sequence is the same.
/// </returns>
public bool Equals(MathProgram other)
{
return(!(other is null) &&
(ReferenceEquals(this, other) ||
this.GetType() == other.GetType() &&
this._hashCode == other._hashCode &&
string.Equals(this.Label, other.Label) &&
this.Input.SequenceEqual(other.Input)));
}
/// <summary>
/// Simplifies the expression of the given <see cref="MathProgram" /> by returning a sub-combination whose fitness is
/// approximately equal to that of the original program by a margin of <paramref name="margin" />, and whose
/// expression is naturally simpler, i.e., has fewer sub-programs.
/// </summary>
/// <returns>An program corresponding to a simplification of the given program.</returns>
/// <param name="program">The program we want to simplify.</param>
/// <param name="fitnessFunction">The fitness function used to determine equivalence.</param>
/// <param name="margin">
/// The acceptable difference between the fitness of the given program and that of a simplified program for them to be
/// considered equivalent.
/// </param>
public static ITreeProgram <double> Simplify(
this MathProgram program, IFitnessFunction <MathProgram> fitnessFunction, double margin = DEFAULT_MARGIN)
{
// gets original program's fitness and count
var simplified = program;
var fitness = fitnessFunction.Evaluate(program);
var length = program.Length;
// first replaces all sub-programs by infinity and NaN recursively
var consts = new HashSet <Constant>
{
new Constant(double.NegativeInfinity),
new Constant(double.NaN),
new Constant(double.PositiveInfinity)
};
bool simplificationFound;
do
{
simplificationFound = false;
var simpLength = simplified.Length;
for (var i = 0u; i < simpLength && !simplificationFound; i++)
{
if (consts.Contains(simplified.ProgramAt(i)))
{
continue;
}
foreach (var constant in consts)
{
var prog = (MathProgram)simplified.Replace(i, constant);
var fit = fitnessFunction.Evaluate(prog);
var progLength = prog.Length;
if (Math.Abs(fit - fitness) < margin && progLength <= length)
{
simplified = prog;
length = progLength;
simplificationFound = true;
break;
}
}
}
} while (simplificationFound);
// then gets all sub-combinations of the simplified program
var alternatives = simplified.GetSubCombinations();
foreach (MathProgram subComb in alternatives)
{
var subFit = fitnessFunction.Evaluate(subComb);
var subCombLength = subComb.Length;
//checks their fitness and count
if (Math.Abs(subFit - fitness) < margin && subCombLength < length)
{
simplified = subComb;
length = subCombLength;
}
}
return(simplified);
}
