add numerical recipes library

lib/nr/ansi/examples/xrkdumb.c

@@ -0,0 +1,45 @@
+
+/* Driver for routine rkdumb */
+
+#include <stdio.h>
+#define NRANSI
+#include "nr.h"
+#include "nrutil.h"
+
+#define NVAR 4
+#define NSTEP 150
+
+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];
+}
+
+extern float **y,*xx;   /* referencing declaration */
+
+int main(void)
+{
+	int j;
+	float x1=1.0,x2=20.0,*vstart;
+
+	vstart=vector(1,NVAR);
+	/* Note: The arrays xx and y must have indices up to NSTEP+1 */
+	xx=vector(1,NSTEP+1);
+	y=matrix(1,NVAR,1,NSTEP+1);
+	vstart[1]=bessj0(x1);
+	vstart[2]=bessj1(x1);
+	vstart[3]=bessj(2,x1);
+	vstart[4]=bessj(3,x1);
+	rkdumb(vstart,NVAR,x1,x2,NSTEP,derivs);
+	printf("%8s %17s %10s\n","x","integrated","bessj3");
+	for (j=10;j<=NSTEP;j+=10)
+		printf("%10.4f %14.6f %12.6f\n",
+			xx[j],y[4][j],bessj(3,xx[j]));
+	free_matrix(y,1,NVAR,1,NSTEP+1);
+	free_vector(xx,1,NSTEP+1);
+	free_vector(vstart,1,NVAR);
+	return 0;
+}
+#undef NRANSI