#355 Warning for non-polynomial algsys

[Stavros Macrakis]

Solve for multiple variables calls Algsys. As it says
(clearly!) in the documentation, this only works for
polynomial equations.

It would be useful, I think, if we would give a warning
(or an error?) when a non-polynomial equation were
passed to algsys, e.g.

(C1) solve(sqrt(a^2+b^2)=0,[a,b])
Warning: Solve/Algsys can only solve for multiple
variables when the equations are polynomial. The
equation sqrt(a^2+b^2)=0 is not polynomial.

(D1) []

This is a common beginner's error, I think, encouraged of
course by the fact that the command is called "solve" --
you'd think it could solve any simple equation....