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

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 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
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