add numerical recipes library

lib/nr/cpp/recipes/polint.cpp

@@ -0,0 +1,34 @@
+#include <cmath>
+#include "nr.h"
+using namespace std;
+
+void NR::polint(Vec_I_DP &xa, Vec_I_DP &ya, const DP x, DP &y, DP &dy)
+{
+	int i,m,ns=0;
+	DP den,dif,dift,ho,hp,w;
+
+	int n=xa.size();
+	Vec_DP c(n),d(n);
+	dif=fabs(x-xa[0]);
+	for (i=0;i<n;i++) {
+		if ((dift=fabs(x-xa[i])) < dif) {
+			ns=i;
+			dif=dift;
+		}
+		c[i]=ya[i];
+		d[i]=ya[i];
+	}
+	y=ya[ns--];
+	for (m=1;m<n;m++) {
+		for (i=0;i<n-m;i++) {
+			ho=xa[i]-x;
+			hp=xa[i+m]-x;
+			w=c[i+1]-d[i];
+			if ((den=ho-hp) == 0.0) nrerror("Error in routine polint");
+			den=w/den;
+			d[i]=hp*den;
+			c[i]=ho*den;
+		}
+		y += (dy=(2*(ns+1) < (n-m) ? c[ns+1] : d[ns--]));
+	}
+}