add numerical recipes library

lib/nr/ansi/examples/xrkqs.c

@@ -0,0 +1,55 @@
+
+/* Driver for routine rkqs */
+
+#include <stdio.h>
+#include <math.h>
+#define NRANSI
+#include "nr.h"
+#include "nrutil.h"
+
+#define N 4
+
+void derivs(float x,float y[],float dydx[])
+{
+	dydx[1] = -y[2];
+	dydx[2]=y[1]-(1.0/x)*y[2];
+	dydx[3]=y[2]-(2.0/x)*y[3];
+	dydx[4]=y[3]-(3.0/x)*y[4];
+}
+
+int main(void)
+{
+	int i,j;
+	float eps,hdid,hnext,htry,x=1.0,*y,*dydx,*dysav,*ysav,*yscal;
+
+	y=vector(1,N);
+	dydx=vector(1,N);
+	dysav=vector(1,N);
+	ysav=vector(1,N);
+	yscal=vector(1,N);
+	ysav[1]=bessj0(x);
+	ysav[2]=bessj1(x);
+	ysav[3]=bessj(2,x);
+	ysav[4]=bessj(3,x);
+	derivs(x,ysav,dysav);
+	for (i=1;i<=N;i++) yscal[i]=1.0;
+	htry=0.6;
+	printf("%10s %11s %12s %13s\n","eps","htry","hdid","hnext");
+	for (i=1;i<=15;i++) {
+		eps=exp((double) -i);
+		x=1.0;
+		for (j=1;j<=N;j++) {
+			y[j]=ysav[j];
+			dydx[j]=dysav[j];
+		}
+		rkqs(y,dydx,N,&x,htry,eps,yscal,&hdid,&hnext,derivs);
+		printf("%13f %8.2f %14.6f %12.6f \n",eps,htry,hdid,hnext);
+	}
+	free_vector(yscal,1,N);
+	free_vector(ysav,1,N);
+	free_vector(dysav,1,N);
+	free_vector(dydx,1,N);
+	free_vector(y,1,N);
+	return 0;
+}
+#undef NRANSI