One or more output arguments not assigned during call to 'C:

One or more output arguments not assigned during call to 'C:\matlab7.0\work\SOR.m (SOR)'.
function [x,k]=SORmethod(A,b,w)
% A:线性方程组左端矩阵
% b:线性方程组右端向量
% x0:迭代初值
% N:迭代次数上界,若迭代次数大于n,则迭代失败
% emg:精度指标
% w:松弛因子
% x:用迭代法求得的线性方程组的近似解
if w>=2
error('A Sor factor must be oppsitive and less than 2');
end
r=10e-6;
N=1000;
[m,n]=size(A);
X=zeros(n,1);
k=1;
while k