add numerical recipes library

lib/nr/ansi/examples/xbrent.c

@@ -0,0 +1,47 @@
+
+/* Driver for routine brent */
+
+#include <stdio.h>
+#include <math.h>
+#define NRANSI
+#include "nr.h"
+
+#define TOL 1.0e-6
+#define EQL 1.0e-4
+
+float func(float x)
+{
+	return bessj0(x);
+}
+
+int main(void)
+{
+	int i,iflag,j,nmin=0;
+	float ax,bx,cx,fa,fb,fc,xmin,bren,amin[21];
+
+	printf("\nMinima of the function bessj0\n");
+	printf("%10s %8s %17s %12s\n","min. #","x","bessj0(x)","bessj1(x)");
+	for (i=1;i<=100;i++) {
+		ax=i;
+		bx=i+1.0;
+		mnbrak(&ax,&bx,&cx,&fa,&fb,&fc,func);
+		bren=brent(ax,bx,cx,func,TOL,&xmin);
+		if (nmin == 0) {
+			amin[1]=xmin;
+			nmin=1;
+			printf("%7d %15.6f %12.6f %12.6f\n",
+				nmin,xmin,bessj0(xmin),bessj1(xmin));
+		} else {
+			iflag=0;
+			for (j=1;j<=nmin;j++)
+				if (fabs(xmin-amin[j]) <= (EQL*xmin)) iflag=1;
+			if (iflag == 0) {
+				amin[++nmin]=xmin;
+				printf("%7d %15.6f %12.6f %12.6f\n",
+					nmin,xmin,bessj0(xmin),bessj1(xmin));
+			}
+		}
+	}
+	return 0;
+}
+#undef NRANSI