add numerical recipes library

lib/nr/cpp/recipes/shell.cpp

@@ -0,0 +1,26 @@
+#include "nr.h"
+
+void NR::shell(const int m, Vec_IO_DP &a)
+{
+	int i,j,inc;
+	DP v;
+
+	inc=1;
+	do {
+		inc *= 3;
+		inc++;
+	} while (inc <= m);
+	do {
+		inc /= 3;
+		for (i=inc;i<m;i++) {
+			v=a[i];
+			j=i;
+			while (a[j-inc] > v) {
+				a[j]=a[j-inc];
+				j -= inc;
+				if (j < inc) break;
+			}
+			a[j]=v;
+		}
+	} while (inc > 1);
+}