【求助】生成复矩阵出错

[yueyue1612]

高手请指教，
我在使用matlab时，刚开始都很正常，突然间，前一时刻，敲入a=j*randn(5,2)+randn(5,2)，运行正常，下一时刻再敲a=j*randn(5,2)+randn(5,2)，报错：“??? Error using ==> mtimes Inner matrix dimensions must agree.”
我重启过matlab，一开始，还能运行成功，没一会再执行相同的生成指令，又报：“??? Error using ==> mtimes Inner matrix dimensions must agree.”

请指点！谢谢！！
>> a=j*randn(5,2)+randn(5,2)

a =

-0.3306 + 0.8057i -0.8468 + 1.4789i
-0.8436 + 0.2316i -0.2463 + 1.1380i
0.4978 - 0.9898i 0.6630 - 0.6841i
1.4885 + 1.3396i -0.8542 - 1.2919i
-0.5465 + 0.2895i -1.2013 - 0.0729i

>> b=j*randn(5,2)+randn(5,2)
??? Error using ==> mtimes
Inner matrix dimensions must agree.