add numerical recipes library

lib/nr/ansi/examples/xmidpnt.c

@@ -0,0 +1,37 @@
+
+/* Driver for routine midpnt */
+
+#include <stdio.h>
+#include <math.h>
+#define NRANSI
+#include "nr.h"
+
+#define NMAX 10
+
+/* Test function */
+float func(float x)
+{
+	return 1.0/sqrt(x);
+}
+
+/* Integral of test function */
+float fint(float x)
+{
+	return 2.0*sqrt(x);
+}
+
+int main(void)
+{
+	float a=0.0,b=1.0,s;
+	int i;
+
+	printf("\nIntegral of func computed with MIDPNT\n");
+	printf("Actual value of integral is %7.4f\n",(fint(b)-fint(a)));
+	printf("%6s %29s \n","n","Approx. integral");
+	for (i=1;i<=NMAX;i++) {
+		s=midpnt(func,a,b,i);
+		printf("%6d %24.6f\n",i,s);
+	}
+	return 0;
+}
+#undef NRANSI