On Fri, Oct 24, 2008 at 9:56 PM, Richard Hennessy <rvh2007 at comcast.net>wrote:
> ...It seems to me that assume_pos is a patch to "fix" a much deeper problem
> with Maxima's asksign. It is not a very good
> one.
>
I absolutely agree that assume_pos is a terrible hack and very likely to
cause problems. It would probably be a good idea to include some sort of
warning in the documentation making that explicit.
> You can get into trouble even if you read the documentation.
>
? The documentation seems pretty clear: assume_pos tells Maxima to assume
that all unknown variables are positive. If this is a safe assumption,
fine. If not, you will get into trouble. A simpler example along the same
lines:
assume_pos: true$
ex: abs(x) => x
ex, x=-5 => -5
Oh, horrors! abs(x) can never be -5! But assume_pos:true asserts that x
cannot be negative. Maxima relied on the assertion. Is that Maxima's fault
or the user's?
-s