add numerical recipes library

lib/nr/ansi/examples/xzbrak.c

@@ -0,0 +1,37 @@
+
+/* Driver for routine zbrak */
+
+#include <stdio.h>
+#define NRANSI
+#include "nr.h"
+#include "nrutil.h"
+
+#define N 100
+#define NBMAX 20
+#define X1 1.0
+#define X2 50.0
+
+static float fx(float x)
+{
+	return bessj0(x);
+}
+
+int main(void)
+{
+	int i,nb=NBMAX;
+	float *xb1,*xb2;
+
+	xb1=vector(1,NBMAX);
+	xb2=vector(1,NBMAX);
+	zbrak(fx,X1,X2,N,xb1,xb2,&nb);
+	printf("\nbrackets for roots of bessj0:\n");
+	printf("%21s %10s %16s %10s\n","lower","upper","f(lower)","f(upper)");
+	for (i=1;i<=nb;i++)
+		printf("%s %2d  %10.4f %10.4f %3s %10.4f %10.4f\n",
+			"  root ",i,xb1[i],xb2[i]," ",
+			fx(xb1[i]),fx(xb2[i]));
+	free_vector(xb2,1,NBMAX);
+	free_vector(xb1,1,NBMAX);
+	return 0;
+}
+#undef NRANSI