求助：solve自动忽略多余自变量。

我应该

syms x y z
[x,z,y]=solve(x+y==1,x-y==2,x,z,y);
if isempty(z)
z=0
end
double(x)
double(z)
double(y)


会报错：

警告: 2 equations in 3 variables. New variables might be introduced.
> In D:\Program Files\MATLAB\R2014a\toolbox\symbolic\symbolic\symengine.p>symengine at 56
  In mupadengine.mupadengine>mupadengine.evalin at 97
  In mupadengine.mupadengine>mupadengine.feval at 150
  In solve at 170
警告: The solutions are parametrized by the symbols:
z1 = C_

> In solve at 190


ans =


    1.5000


错误使用 mupadmex
Error in MuPAD command: DOUBLE cannot convert the input expression into a double array.
If the input expression contains a symbolic variable, use the VPA function instead.


出错 sym/double (line 514)
        Xstr = mupadmex('symobj::double', S.s, 0);

pandaquan0

是因为在for循环中，某些循环会正好消掉某个自变量。所以有此一问。
上面的函数是类比。z如果正好消掉，把z赋值成0.