Changing signs of terms like (x-1) after factor or simplification

Sorry!  I sent you the wrong version of my code.

Try:

pullsign(ex) :=
  (ex: postrans(ex),
   if member(sign(ex), '[neg, nz])
   then [-1, -ex]
   else [1, ex])$

postrans(ex):=
  block([inflag:true,pull],
    if mapatom(ex) then ex
    elseif op(ex)="*" then
       (pull:maplist(pullsign,ex),
        apply("*",map('first,pull))*apply("*",map('second,pull)))
    elseif op(ex)="^" then
       (pull:pullsign(part(ex,1)),
        pull[1]^part(ex,2)*pull[2]^part(ex,2))
    else map(postrans,ex))$

By the way, you may want to update to the current version of Maxima -- I am
testing on 5.23.2.

              -s

On Sat, Mar 26, 2011 at 21:07, Sebastian Kranz <skranz at uni-bonn.de> wrote:

>  Dear Stavros,
>
> thanks a lot, I was indeed looking for such a function. It worked very nice
> on example factorizations that I tested. E.g.
>
>
> assume(x>=0,x<=1)$
> postrans(factor(a*x-a));
>
> yields as desired
>                             - a (1 - x)
>
> even though I just have weak inequalities in assume(...). Interestingly,
> however, I could not replicate your example.  This means
>
>
> assume(x>0,x<1)$
> postrans((1-x)*(x-1)^3);
>
> yields on my Computer without any change
>
>
> (1-x)*(x-1)^3
>
> and
>
>
> assume(x>0,x<1)$
> postrans(5*factor((1-x)*(x-1)^3));
>
> yields
>
> - 5 (x - 1)^4
>
> Maybe some of my global settings are different than yours (I have got
> Maxima 5.18.1 for Windows). Still the function will be very helpful, as it
> works in a lot of cases.
>
> Many thanks,
> Sebastian
>
>
>
> Am 26.3.2011 21:23, schrieb Stavros Macrakis:
>
> How about something like this:
>
>  pullsign(ex) :=
>    if member(sign(ex), '[neg, nz])
>    then [-1, -ex]
>    else [1, ex]$
>
>  postrans(ex):=
>   block([inflag:true,pull],
>     if mapatom(ex) then ex
>     elseif op(ex)="*" then
>        (pull:maplist(pullsign,ex),
>         apply("*",map('first,pull))*apply("*",map('second,pull)))
>     elseif op(ex)="^" then
>        (pull:pullsign(part(ex,1)),
>         pull[1]^part(ex,2)*pull[2]^part(ex,2))
>     else map(postrans,ex))$
>
>  Example:
>
>       assume(x>0,x<1)$
>
>       postrans((1-x)*(x-1)^3)  =>  -(1-x)^4
>
>  Note that this won't work for a single term:
>
>       postrans(-(1-x)) => x-1
>
>  Is this what you had in mind?
>
>             -s
>
>
>  On Sat, Mar 26, 2011 at 11:47, Sebastian Kranz <skranz at uni-bonn.de>wrote:
>
>> Hi,
>>
>>  I use Maxima often to simplify terms or equations that have a lot terms
>> of the form (1-x) with variables x in [0,1]. The simplifying functions of
>> Maxima tend to transform the terms (1-x) in the less intuitive form -(x-1)
>> and I have to convert them back manually. For example,
>>
>> (%i231) factor(a-x*a);
>> (%o231) - a (x - 1)
>>
>> Does anybody know an automatic way to tell Maxima that it shall tranform
>> terms like (x-1) into -(1-x) and multiply the minus sign with all other
>> minus signs in the product? E.g. I would like
>>
>> factor(a-x*a);
>> a (1-x)
>>
>> or
>>
>> factor(-a+x*a);
>> - a (1-x)
>>
>> Alternatively, is it complicated to write a general function that does
>> this transformation? E.g. a function nicesign(expr), yielding:
>>
>> nicesign(factor(a-x*a));
>> a (1-x)
>>
>> Perhaps creating such a function is not too complciated, but I really have
>> no knowledge of maxima programming.
>>
>> Thanks for any help,
>> Sebastian
>>
>>
>> _______________________________________________
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>>
>
>
>