add numerical recipes library

lib/nr/ansi/examples/xratint.c

@@ -0,0 +1,41 @@
+
+/* Driver for routine ratint */
+
+#include <stdio.h>
+#include <math.h>
+#define NRANSI
+#include "nr.h"
+#include "nrutil.h"
+
+#define NPT 6
+#define EPS 1.0
+
+float f(float x,float eps)
+{
+	return x*exp(-x)/(SQR(x-1.0)+eps*eps);
+}
+
+int main(void)
+{
+	int i;
+	float dyy,xx,yexp,yy,*x,*y;
+
+	x=vector(1,NPT);
+	y=vector(1,NPT);
+	for (i=1;i<=NPT;i++) {
+		x[i]=i*2.0/NPT;
+		y[i]=f(x[i],EPS);
+	}
+	printf("\nDiagonal rational function interpolation\n");
+	printf("\n%5s %13s %14s %12s\n","x","interp.","accuracy","actual");
+	for (i=1;i<=10;i++) {
+		xx=0.2*i;
+		ratint(x,y,NPT,xx,&yy,&dyy);
+		yexp=f(xx,EPS);
+		printf("%6.2f %12.6f    %11f %13.6f\n",xx,yy,dyy,yexp);
+	}
+	free_vector(y,1,NPT);
+	free_vector(x,1,NPT);
+	return 0;
+}
+#undef NRANSI