add numerical recipes library

lib/nr/ansi/examples/xstiff.c

@@ -0,0 +1,31 @@
+
+/* Driver for routine stiff */
+
+#include <stdio.h>
+#define NRANSI
+#include "nr.h"
+#include "nrutil.h"
+
+int kmax,kount;        /* defining declarations */
+float *xp,**yp,dxsav;
+
+int main(void)
+{
+	float eps,hstart,x1=0.0,x2=50.0,y[4];
+	int nbad,nok;
+
+	for (;;) {
+		printf("Enter eps,hstart\n");
+		if (scanf("%f %f",&eps,&hstart) == EOF) break;
+		kmax=0;
+		y[1]=y[2]=1.0;
+		y[3]=0.0;
+		odeint(y,3,x1,x2,eps,hstart,0.0,&nok,&nbad,derivs,stiff);
+		printf("\n%s %13s %3d\n","successful steps:"," ",nok);
+		printf("%s %20s %3d\n","bad steps:"," ",nbad);
+		printf("Y(END) = %12.6f %12.6f %12.6f\n",y[1],y[2],y[3]);
+	}
+	printf("Normal completion\n");
+	return 0;
+}
+#undef NRANSI