add numerical recipes library

lib/nr/k_and_r/recipes/sprstx.c

@@ -0,0 +1,17 @@
+
+void sprstx(sa,ija,x,b,n)
+float b[],sa[],x[];
+unsigned long ija[],n;
+{
+	void nrerror();
+	unsigned long i,j,k;
+
+	if (ija[1] != n+2) nrerror("mismatched vector and matrix in sprstx");
+	for (i=1;i<=n;i++) b[i]=sa[i]*x[i];
+	for (i=1;i<=n;i++) {
+		for (k=ija[i];k<=ija[i+1]-1;k++) {
+			j=ija[k];
+			b[j] += sa[k]*x[i];
+		}
+	}
+}