add numerical recipes library

lib/nr/ansi/recipes/chebft.c

@@ -0,0 +1,29 @@
+
+#include <math.h>
+#define NRANSI
+#include "nrutil.h"
+#define PI 3.141592653589793
+
+void chebft(float a, float b, float c[], int n, float (*func)(float))
+{
+	int k,j;
+	float fac,bpa,bma,*f;
+
+	f=vector(0,n-1);
+	bma=0.5*(b-a);
+	bpa=0.5*(b+a);
+	for (k=0;k<n;k++) {
+		float y=cos(PI*(k+0.5)/n);
+		f[k]=(*func)(y*bma+bpa);
+	}
+	fac=2.0/n;
+	for (j=0;j<n;j++) {
+		double sum=0.0;
+		for (k=0;k<n;k++)
+			sum += f[k]*cos(PI*j*(k+0.5)/n);
+		c[j]=fac*sum;
+	}
+	free_vector(f,0,n-1);
+}
+#undef PI
+#undef NRANSI