create example dir

examples/polyapprox.cpp

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+#include <cstdio>
+#include <cmath>
+
+#include "de.h"
+
+// the order of the polynomial (actually the number of coefficients, i.e. 1 = constant, 2 = line, etc.)
+#define NUM_COEFFICIENTS 8
+
+// the function we're searching for
+double TargetFunction(double x)
+{
+	return 1.0 / (1.0 + exp(-4.9*x));               // Ken Stanley's NEAT activation
+	//return (1.0 / (1.0 + exp(-4.9*x)) - 0.5) * 2.0; // " " (signed version)
+	//return (1.0 / (1.0 + exp(-x)) - 0.5) * 2.0;     // signed sigmoid
+	//return exp(-x*x);                               // gaussian
+	//return tanh(x);                                 // tanh
+	//return (2.0/(1.0+exp(-x))-1.0);                 // tanh approximation
+	//return (x<0.0 ? -1.0 : 1.0) * sqrt(abs(x));     // signed root
+	//return sin(x);                                  // sin
+}
+
+
+// a helper function used in calculating the polynomials
+double CalculatePolynomial(double x, int n_coeffs, const double coeffs[])
+{
+	double accum = 0.0;
+	double xmul  = 1.0;
+	for (int i = n_coeffs-1; i>=0; --i)
+	{
+		accum += xmul * coeffs[i];
+		xmul *= x;
+	}
+	return accum;
+}
+
+
+// our DE implementation
+class PolySearch: public DE::Engine<NUM_COEFFICIENTS>
+{
+	public:
+		// this method is called by the DE::Engine::Solve() to test a single DE individual
+		double TestFitness(const double testcase[NUM_COEFFICIENTS], bool& stop)
+		{
+			ErrorAccumulator e;
+
+			// accumulate squared error
+			for ( double i=-1.25;i<=1.25;i+=0.001 )
+			{
+				// test
+				double actual   = CalculatePolynomial(i,NUM_COEFFICIENTS,testcase);
+				double expected = TargetFunction(i);
+
+				// accumulate error
+				e.AddTestCase(expected, actual);
+			}
+
+			// set stop flag if the error is really low
+			if ( e.GetRMSE() < 0.0000001 )
+			{
+				stop = true;
+			}
+
+			// done
+			return e.GetRMSE();
+		}
+};
+
+
+// main program
+int main()
+{
+	PolySearch de;
+
+	// setup, adjust from default range
+	de.SetRange(-0.1,0.1);
+
+	// create new population with adjusted range
+	de.Reset();
+
+	// run the DE
+	de.Solve(1500);
+
+	// output winner in polynomial form
+	printf("Best Polynomial Found\n=====================\ny =");
+	for (int i=0;i<NUM_COEFFICIENTS-2;++i)
+	{
+		printf(" %0.16f*x^%d +",de.GetBest()[i],NUM_COEFFICIENTS-1-i);
+	}
+	printf(" %0.16f*x + %0.16f\n",de.GetBest()[NUM_COEFFICIENTS-2],de.GetBest()[NUM_COEFFICIENTS-1]);
+
+	// done
+	return 0;
+}