Re: Bug in Calc?

[Jay Belanger <belanger@truman.edu>]

Neon Absentius <absent@sdf.lonestar.org> writes:

> On Tue, Sep 06, 2005 at 09:33:48PM +0000, Neon Absentius wrote:
>
>> there seems to be a bug: After I give 'm v' if I ask calc to
>> simplify the expression 'a b - b a' it leaves it as is which is as 
>> expected. However when I ask it to expand '(a+b)^2' it returns 
>> 'a^2 + 2 b a + b^2' which is of course wrong if a and b don't commute. 
>> This happens both with emacs-multi-tty (22.0.50) and whith emacs
>> 21.4.1 on a Debian testing/unstable. The bug manifsts itself also
>> for the expansion of '(a+b)^3' however calc expands '(x+y)(x-y)'
>> into 'x^2 + y x  -  x y + y^2'. Strange!
>
> Maybe not so strange.

Maybe not strange, but still a bug.

> Probably calc uses formulae (the binomial expansion?)  to expand the
> power instead of fully distributing the multiplication over the
> addtition "by hand", so to speak.  Of course the binomial expansion
> is not valid if the variables involved do not commute.

That is what happens.  It should be fixed soon.

Jay