add numerical recipes library

lib/nr/k_and_r/recipes/pcshft.c

@@ -0,0 +1,19 @@
+
+void pcshft(a,b,d,n)
+float a,b,d[];
+int n;
+{
+	int k,j;
+	float fac,cnst;
+
+	cnst=2.0/(b-a);
+	fac=cnst;
+	for (j=1;j<n;j++) {
+		d[j] *= fac;
+		fac *= cnst;
+	}
+	cnst=0.5*(a+b);
+	for (j=0;j<=n-2;j++)
+		for (k=n-2;k>=j;k--)
+			d[k] -= cnst*d[k+1];
+}