add numerical recipes library

lib/nr/ansi/recipes/snrm.c

@@ -0,0 +1,20 @@
+
+#include <math.h>
+
+double snrm(unsigned long n, double sx[], int itol)
+{
+	unsigned long i,isamax;
+	double ans;
+
+	if (itol <= 3) {
+		ans = 0.0;
+		for (i=1;i<=n;i++) ans += sx[i]*sx[i];
+		return sqrt(ans);
+	} else {
+		isamax=1;
+		for (i=1;i<=n;i++) {
+			if (fabs(sx[i]) > fabs(sx[isamax])) isamax=i;
+		}
+		return fabs(sx[isamax]);
+	}
+}