add numerical recipes library

lib/nr/cpp/recipes/splint.cpp

@@ -0,0 +1,22 @@
+#include "nr.h"
+
+void NR::splint(Vec_I_DP &xa, Vec_I_DP &ya, Vec_I_DP &y2a, const DP x, DP &y)
+{
+	int k;
+	DP h,b,a;
+
+	int n=xa.size();
+	int klo=0;
+	int khi=n-1;
+	while (khi-klo > 1) {
+		k=(khi+klo) >> 1;
+		if (xa[k] > x) khi=k;
+		else klo=k;
+	}
+	h=xa[khi]-xa[klo];
+	if (h == 0.0) nrerror("Bad xa input to routine splint");
+	a=(xa[khi]-x)/h;
+	b=(x-xa[klo])/h;
+	y=a*ya[klo]+b*ya[khi]+((a*a*a-a)*y2a[klo]
+		+(b*b*b-b)*y2a[khi])*(h*h)/6.0;
+}