When I wrote conjugate.lisp, there was a rudimentary csign (not
$csign) function. Given the limitations of $sign and the (extreme)
difficultly in working with code in compar.lisp, your work on $csign
improved Maxima a great deal--I didn't mean to imply anything negative
about the function $csign.
The other day when I gave the sign function object-oriented dispatch,
I thought (not long) about appending code that would do a better job
of determining the sign of a single variable polynomial. For a
polynomial defined on the entire reals, a few lines of code with
nroots might work, but for a polynomial defined on a subset of the
reals, it's not easy to determine from the fact database lower and
upper bounds for a variable (suppose x+y<2 and x-y>5, deduce y <-3/2).
It would be great if the fact database would maintain bunch of
derived facts--re-deriving them each time sign is called is too spendy, I
think.
--Barton
-----maxima-bounces at math.utexas.edu wrote: -----
>the?time?you?wrote?the?code?of?conjugate.lisp?the?function?$csign?was
>not?present.?The?first?commit?of?$csign?I?have?done?in?Dezember?2008.
>The?functionality?of?$csign?is?not?perfect,?but?it?is?supposed?to?extend
>the?function?$sign?in?a?way?which?does?not?change?any?old?code.