create example dir

examples/piecewiseapprox.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 7
+
+// 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 CalculatePiecewise(double x, int n_coeffs, const double coeffs[])
+{
+	double abs_x = (x < 0.0 ? -x : x);
+	const double* pcoeffs;
+	if ( abs_x < coeffs[6] )
+		pcoeffs = &coeffs[0];
+	else
+		pcoeffs = &coeffs[3];
+
+	return (pcoeffs[0] + pcoeffs[1]*abs_x + pcoeffs[2]*abs_x*abs_x) * (x < 0.0 ? -1.0 : 1.0);
+}
+
+
+// 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=-2.5;i<=2.5;i+=0.01 )
+			{
+				// test
+				double actual   = CalculatePiecewise(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);
+
+	// reset, and run the DE
+	de.Solve(1000);
+
+	// done
+	return 0;
+}