matlab--?Error using ==> mtimes Inner matrix dimensions must

matlab--?Error using ==> mtimes Inner matrix dimensions must agree.
x=[ones(1,10) zeros(1,41)];
n=1:50;k=-25:25;W=(pi/12.5)*k;f=(1/25)*k*1000;
X=x*(exp(-j*pi/12.5)).^(n'*k);magX=abs(X);
subplot(3,2,2);stem(x);title('输入信号x[n]');subplot(3,2,3);stem(f,magX);title('X频');
Error using ==> mtimes
Inner matrix dimensions must agree.