add numerical recipes library

lib/nr/ansi/examples/xmmid.c

@@ -0,0 +1,56 @@
+
+/* Driver for routine mmid */
+
+#include <stdio.h>
+#define NRANSI
+#include "nr.h"
+#include "nrutil.h"
+
+#define NVAR 4
+#define X1 1.0
+#define HTOT 0.5
+
+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;
+	float b1,b2,b3,b4,xf=X1+HTOT,*y,*yout,*dydx;
+
+	y=vector(1,NVAR);
+	yout=vector(1,NVAR);
+	dydx=vector(1,NVAR);
+	y[1]=bessj0(X1);
+	y[2]=bessj1(X1);
+	y[3]=bessj(2,X1);
+	y[4]=bessj(3,X1);
+	derivs(X1,y,dydx);
+	b1=bessj0(xf);
+	b2=bessj1(xf);
+	b3=bessj(2,xf);
+	b4=bessj(3,xf);
+	printf("First four Bessel functions:\n");
+	for (i=5;i<=50;i+=5) {
+		mmid(y,dydx,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","bessj");
+		printf("%12.6f %12.6f\n",yout[1],b1);
+		printf("%12.6f %12.6f\n",yout[2],b2);
+		printf("%12.6f %12.6f\n",yout[3],b3);
+		printf("%12.6f %12.6f\n",yout[4],b4);
+		printf("\nPress RETURN to continue...\n");
+		(void) getchar();
+	}
+	free_vector(dydx,1,NVAR);
+	free_vector(yout,1,NVAR);
+	free_vector(y,1,NVAR);
+	return 0;
+}
+#undef NRANSI