求助：solve自动忽略多余自变量。

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);