add numerical recipes library

lib/nr/cpp/recipes/chebft.cpp

@@ -0,0 +1,26 @@
+#include <cmath>
+#include "nr.h"
+using namespace std;
+
+void NR::chebft(const DP a, const DP b, Vec_O_DP &c, DP func(const DP))
+{
+	const DP PI=3.141592653589793;
+	int k,j;
+	DP fac,bpa,bma,y,sum;
+
+	int n=c.size();
+	Vec_DP f(n);
+	bma=0.5*(b-a);
+	bpa=0.5*(b+a);
+	for (k=0;k<n;k++) {
+		y=cos(PI*(k+0.5)/n);
+		f[k]=func(y*bma+bpa);
+	}
+	fac=2.0/n;
+	for (j=0;j<n;j++) {
+		sum=0.0;
+		for (k=0;k<n;k++)
+			sum += f[k]*cos(PI*j*(k+0.5)/n);
+		c[j]=fac*sum;
+	}
+}