add numerical recipes library

lib/nr/cpp/recipes/vander.cpp

@@ -0,0 +1,31 @@
+#include "nr.h"
+
+void NR::vander(Vec_I_DP &x, Vec_O_DP &w, Vec_I_DP &q)
+{
+	int i,j,k;
+	DP b,s,t,xx;
+
+	int n=q.size();
+	Vec_DP c(n);
+	if (n == 1) w[0]=q[0];
+	else {
+		for (i=0;i<n;i++) c[i]=0.0;
+		c[n-1] = -x[0];
+		for (i=1;i<n;i++) {
+			xx = -x[i];
+			for (j=(n-1-i);j<(n-1);j++) c[j] += xx*c[j+1];
+			c[n-1] += xx;
+		}
+		for (i=0;i<n;i++) {
+			xx=x[i];
+			t=b=1.0;
+			s=q[n-1];
+			for (k=n-1;k>0;k--) {
+				b=c[k]+xx*b;
+				s += q[k-1]*b;
+				t=xx*t+b;
+			}
+			w[i]=s/t;
+		}
+	}
+}