add numerical recipes library

lib/nr/ansi/examples/xexpdev.c

@@ -0,0 +1,39 @@
+
+/* Driver for routine expdev */
+
+#include <stdio.h>
+#include <math.h>
+#define NRANSI
+#include "nr.h"
+
+#define NPTS 10000
+#define EE 2.718281828
+
+int main(void)
+{
+	long idum=(1);
+	int i,j,total=0,x[21];
+	float expect,xx,y,trig[21];
+
+	for (i=0;i<=20;i++) {
+		trig[i]=i/20.0;
+		x[i]=0;
+	}
+	for (i=1;i<=NPTS;i++) {
+		y=expdev(&idum);
+		for (j=1;j<=20;j++)
+			if ((y < trig[j]) && (y > trig[j-1])) ++x[j];
+	}
+	for (i=1;i<=20;i++) total += x[i];
+	printf("\nexponential distribution with %7d points\n",NPTS);
+	printf("    interval      observed     expected\n\n");
+	for (i=1;i<=20;i++) {
+		xx=(float) x[i]/total;
+		expect=exp(-(trig[i-1]+trig[i])/2.0);
+		expect *= (0.05*EE/(EE-1));
+		printf("%6.2f %6.2f %12.6f %12.6f \n",
+			trig[i-1],trig[i],xx,expect);
+	}
+	return 0;
+}
+#undef NRANSI