add numerical recipes library

lib/nr/ansi/examples/xspline.c

@@ -0,0 +1,41 @@
+
+/* Driver for routine spline */
+
+#include <stdio.h>
+#include <math.h>
+#define NRANSI
+#include "nr.h"
+#include "nrutil.h"
+
+#define N 20
+#define PI 3.1415926
+
+int main(void)
+{
+	int i;
+	float yp1,ypn,*x,*y,*y2;
+
+	x=vector(1,N);
+	y=vector(1,N);
+	y2=vector(1,N);
+	printf("\nsecond-derivatives for sin(x) from 0 to pi\n");
+	/* Generate array for interpolation */
+	for (i=1;i<=20;i++) {
+		x[i]=i*PI/N;
+		y[i]=sin(x[i]);
+	}
+	/* calculate 2nd derivative with spline */
+	yp1=cos(x[1]);
+	ypn=cos(x[N]);
+	spline(x,y,N,yp1,ypn,y2);
+	/* test result */
+	printf("%23s %16s\n","spline","actual");
+	printf("%11s %14s %16s\n","angle","2nd deriv","2nd deriv");
+	for (i=1;i<=N;i++)
+		printf("%10.2f %16.6f %16.6f\n",x[i],y2[i],-sin(x[i]));
+	free_vector(y2,1,N);
+	free_vector(y,1,N);
+	free_vector(x,1,N);
+	return 0;
+}
+#undef NRANSI