add numerical recipes library

lib/nr/ansi/examples/xzbrac.c

@@ -0,0 +1,31 @@
+
+/* Driver for routine zbrac */
+
+#include <stdio.h>
+#define NRANSI
+#include "nr.h"
+
+static float fx(float x)
+{
+	return bessj0(x);
+}
+
+int main(void)
+{
+	int succes,i;
+	float x1,x2;
+
+	printf("%21s %23s\n","bracketing values:","function values:");
+	printf("%6s %10s %21s %12s\n","x1","x2","bessj0(x1)","bessj0(x2)");
+	for (i=1;i<=10;i++) {
+		x1=i;
+		x2=x1+1.0;
+		succes=zbrac(fx,&x1,&x2);
+		if (succes) {
+			printf("%7.2f %10.2f %6s %12.6f %12.6f \n",
+				x1,x2," ",fx(x1),fx(x2));
+		}
+	}
+	return 0;
+}
+#undef NRANSI