add numerical recipes library

lib/nr/ansi/examples/xdfridr.c

@@ -0,0 +1,27 @@
+
+/* Driver for routine dfridr */
+
+#include <stdio.h>
+#include <math.h>
+#define NRANSI
+#include "nr.h"
+#include "nrutil.h"
+
+float func(float x)
+{
+	return tan(x);
+}
+
+int main(void)
+{
+	float x,h,dx,err;
+
+	printf("input x, h\n");
+	while (scanf("%f %f",&x,&h) != EOF) {
+		dx=dfridr(func,x,h,&err);
+		printf("dfridr=%12.6f %12.6f %12.6f\n",dx,1.0/SQR(cos(x)),err);
+	}
+
+	return 0;
+}
+#undef NRANSI