add numerical recipes library

lib/nr/k_and_r/recipes/lubksb.c

@@ -0,0 +1,23 @@
+
+void lubksb(a,n,indx,b)
+float **a,b[];
+int *indx,n;
+{
+	int i,ii=0,ip,j;
+	float sum;
+
+	for (i=1;i<=n;i++) {
+		ip=indx[i];
+		sum=b[ip];
+		b[ip]=b[i];
+		if (ii)
+			for (j=ii;j<=i-1;j++) sum -= a[i][j]*b[j];
+		else if (sum) ii=i;
+		b[i]=sum;
+	}
+	for (i=n;i>=1;i--) {
+		sum=b[i];
+		for (j=i+1;j<=n;j++) sum -= a[i][j]*b[j];
+		b[i]=sum/a[i][i];
+	}
+}