add numerical recipes library

lib/nr/ansi/examples/xzbrent.c

@@ -0,0 +1,38 @@
+
+/* Driver for routine zbrent */
+
+#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 tol,root,*xb1,*xb2;
+
+	xb1=vector(1,NBMAX);
+	xb2=vector(1,NBMAX);
+	zbrak(fx,X1,X2,N,xb1,xb2,&nb);
+	printf("\nRoots of bessj0:\n");
+	printf("%21s %15s\n","x","f(x)");
+	for (i=1;i<=nb;i++) {
+		tol=(1.0e-6)*(xb1[i]+xb2[i])/2.0;
+		root=zbrent(fx,xb1[i],xb2[i],tol);
+		printf("root %3d %14.6f %14.6f\n",i,root,fx(root));
+	}
+	free_vector(xb2,1,NBMAX);
+	free_vector(xb1,1,NBMAX);
+	return 0;
+}
+#undef NRANSI