add numerical recipes library

lib/nr/ansi/examples/xstoerm.c

@@ -0,0 +1,60 @@
+
+/* Driver for routine stoerm */
+
+#include <stdio.h>
+#include <math.h>
+#define NRANSI
+#include "nr.h"
+#include "nrutil.h"
+
+#define NVAR 4
+#define X1 0.0
+#define HTOT 1.570796
+
+float d2y1(float x)
+{
+	return sin(x)+x;
+}
+
+float d2y2(float x)
+{
+	return cos(x)+x*x-2;
+}
+
+void derivs(float x,float y[],float dydx[])
+{
+	dydx[1]=x-y[1];
+	dydx[2]=x*x-y[2];
+}
+
+int main(void)
+{
+	int i;
+	float a1,a2,xf,*y,*yout,*d2y;
+
+	y=vector(1,NVAR);
+	yout=vector(1,NVAR);
+	d2y=vector(1,NVAR);
+	y[1]=0.0;
+	y[2] = -1.0;
+	y[3]=2.0;
+	y[4]=0.0;
+	derivs(X1,y,d2y);
+	xf=X1+HTOT;
+	a1=d2y1(xf);
+	a2=d2y2(xf);
+	printf("Stoermer's Rule:\n");
+	for (i=5;i<=45;i+=10) {
+		stoerm(y,d2y,NVAR,X1,HTOT,i,yout,derivs);
+		printf("\n%s %5.2f %s %5.2f %s %2d %s \n",
+			"x=",X1," to ",X1+HTOT," in ",i," steps");
+		printf("%14s %9s\n","integration","answers");
+		printf("%12.6f %12.6f\n",yout[1],a1);
+		printf("%12.6f %12.6f\n",yout[2],a2);
+	}
+	free_vector(d2y,1,NVAR);
+	free_vector(yout,1,NVAR);
+	free_vector(y,1,NVAR);
+	return 0;
+}
+#undef NRANSI