add numerical recipes library

lib/nr/ansi/recipes/vander.c

@@ -0,0 +1,35 @@
+
+#define NRANSI
+#include "nrutil.h"
+
+void vander(double x[], double w[], double q[], int n)
+{
+	int i,j,k;
+	double b,s,t,xx;
+	double *c;
+
+	c=dvector(1,n);
+	if (n == 1) w[1]=q[1];
+	else {
+		for (i=1;i<=n;i++) c[i]=0.0;
+		c[n] = -x[1];
+		for (i=2;i<=n;i++) {
+			xx = -x[i];
+			for (j=(n+1-i);j<=(n-1);j++) c[j] += xx*c[j+1];
+			c[n] += xx;
+		}
+		for (i=1;i<=n;i++) {
+			xx=x[i];
+			t=b=1.0;
+			s=q[n];
+			for (k=n;k>=2;k--) {
+				b=c[k]+xx*b;
+				s += q[k-1]*b;
+				t=xx*t+b;
+			}
+			w[i]=s/t;
+		}
+	}
+	free_dvector(c,1,n);
+}
+#undef NRANSI