Number of equations and symbols do not match in linsolve

[JJShi92]

If the number of equations doesn't equal to the number of symbols, the error "Number of equations and symbols do not match" raises.
However, only when number of equations less than the number of symbols, the solver can not find the soluation.
Only if the number of equations not less than the number of symbols, the solver should still be valid.
I think maybe we can change the condiftion "if syms_.size() != eqs_.size():" to "if syms_.size() > eqs_.size():"