"trigrat" caught in infinite loop - depending on how you call it

The fact that you have to use 'reset' indicates that there is a bug in
trigrat.  It would be better to fix the bug than to try to work around it,
but I suppose you could do a binary search of the settings that 'reset'
resets....

            -s

On Wed, Nov 7, 2012 at 10:46 AM, David Scherfgen <d.scherfgen at googlemail.com
> wrote:

> Thanks for this nice observation.
> I found out that if you call "reset()" inbetween, it gives the short
> answer both times:
>
> f: 1/(y+sqrt(y));
> [trigrat(f), reset(), trigrat(f)];
>
> But I think that "reset()" might be doing a bit too much.
> How could I find the minimum set of settings/variables that I have to
> reset in order to make it work correctly?
>
> - David
>
>
> Am 07.11.2012 16:06, schrieb Stavros Macrakis:
>
>> trigrat apparently leaves some state around after exiting, which is bad...
>>
>> Starting from David's example, here is the simplest bad case I could find:
>>
>> f: 1/(y+sqrt(y))$
>>
>> [trigrat(f),trigrat(f)]  =>  [ <small expression>, <big expression> ]
>>
>> This doesn't lead to an infinite loop, but the two results are different
>> when they should be the same.
>>
>> Tested in 5.27.0 2012-04-30 11:59:06 i686-apple-darwin11.3.0 SBCL
>> 1.0.55.0-abb03f9
>>
>>     -s
>>
>> On Wed, Nov 7, 2012 at 7:28 AM, David Scherfgen <
>> d.scherfgen at googlemail.com <mailto:d.scherfgen@**googlemail.com<d.scherfgen at googlemail.com>>>
>> wrote:
>>
>>     Hello Maxima users,
>>
>>     I have discovered a very strange bug in Maxima, which I am about
>>     to report on SourceForge.
>>     But nevertheless, I want to ask if any of you has come across this
>>     one or might be able to help me circumvent it.
>>
>>     The following works:
>>
>>     e : 2*x/(sqrt(y)+x) - (x^2/((sqrt(y)+x)^2));
>>     trigrat(e);
>>     trigrat(xthru(e));
>>
>>     But when I do this:
>>
>>     ( trigrat(e), trigrat(xthru(e)) )
>>
>>     or
>>
>>     [ trigrat(e), trigrat(xthru(e)) ]
>>
>>     the second "trigrat" call inside will hang, i.e. Maxima will run
>>     on 100% CPU and will never return.
>>     So: evaluating both lines separately works, but evaluating them
>>     together or inside a function will cause the "bug".
>>
>>     Strangely, everything works fine when I swap the expressions:
>>
>>     ( trigrat(e), trigrat(xthru(e)) );   /* loops forever */
>>     ( trigrat(xthru(e)), trigrat(e) );   /* works */
>>
>>     I can't find a pattern ... it seems very mysterious to me.
>>     Any idea what might be happening here?
>>
>>     Regards,
>>     David Scherfgen
>>     ______________________________**_________________
>>     Maxima mailing list
>>     Maxima at math.utexas.edu <mailto:Maxima at math.utexas.edu**>
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>>
>>
>>
>