add numerical recipes library

lib/nr/cpp/recipes/evlmem.cpp

@@ -0,0 +1,21 @@
+#include <cmath>
+#include "nr.h"
+using namespace std;
+
+DP NR::evlmem(const DP fdt, Vec_I_DP &d, const DP xms)
+{
+	int i;
+	DP sumr=1.0,sumi=0.0,wr=1.0,wi=0.0,wpr,wpi,wtemp,theta;
+
+	int m=d.size();
+	theta=6.28318530717959*fdt;
+	wpr=cos(theta);
+	wpi=sin(theta);
+	for (i=0;i<m;i++) {
+		wr=(wtemp=wr)*wpr-wi*wpi;
+		wi=wi*wpr+wtemp*wpi;
+		sumr -= d[i]*wr;
+		sumi -= d[i]*wi;
+	}
+	return xms/(sumr*sumr+sumi*sumi);
+}