今晚 用matlab做多维数组字符运算 对某个维度进行求和 发现sum函数失效 不知哪位仁兄有高见！
例子
>> syms a b c d;
e=[a b;c d];
e1=[a a;c d];
e2=[a b;c c];
f=cat(3,e,e1,e2)
sum(f,1)


f(:,:,1) =

[ a, b]
[ c, d]


f(:,:,2) =

[ a, a]
[ c, d]


f(:,:,3) =

[ a, b]
[ c, c]

??? Error using ==> mupadmex
Error in MuPAD command: unable to define matrix over Dom::ExpressionField() [(Dom::Matrix(Dom::ExpressionField()))::new]

Error in ==> sym.sym>sym.sum at 736
                s = mupadmex('symobj::prodsumdim',A.s,num2str(dim),'_plus');