Search All of the Math Forum:

Views expressed in these public forums are not endorsed by NCTM or The Math Forum.

Topic: Rubi 4.5 released
Replies: 21   Last Post: Jun 29, 2014 4:29 AM

 Search Thread: Advanced Search

 Messages: [ Previous | Next ]
 clicliclic@freenet.de Posts: 1,245 Registered: 4/26/08
Re: Rubi 4.5 released
Posted: Jun 21, 2014 11:06 AM
 Plain Text Reply

Albert Rich schrieb:
>
> On Friday, June 20, 2014 9:38:45 PM UTC-10, clicl...@freenet.de wrote:
>

> > The Rubi 4.5 Utility Functions exhibit a typo in the error message
> > "Warning: Unrecog[]ized expression for expansion".
> >
> > I saw a handful of TimeConstrained[]s in this file, some evidently used
> > to tame MMA's Simplify[]. But you also use this brutal means to protect
> > the recursive FixSimplify[] rule set as well as the recursive functions
> > NormalizeSumFactors[] and ContentFactorAux[], all of which seem entirely
> > under your control. Why is this necessary? Does Rubi have to be
> > prevented from getting lost in the woods of its integration rules in
> > this way too?
> >
> > PS: Another misprint: The integral sign is missing for Example 5 in
> > Chapter 7 of Timofeev's integrals, as found on the Rubi website:

>
> Thank you for reporting the two typos. They have been corrected and
> revised versions of the files posted on Rubi's website.
>
> Unfortunately as a last resort on integrands it does not recognize,
> Rubi sometimes uses integration methods, like partial fraction
> expansion, that can hang the system. Also the simplification of
> recursively derived integrands can hang the system. Therefore, Rubi
> uses the TimeConstrained function to regain control after a fixed,
> somewhat arbitrary amount of time. Elimination of such hacks depends
> on finding rules that clearly result in simpler integrands -- a never
> ending and fascinating quest...
>

Hmmm. How about checking the number of unevaluated Int[]s in your
expression at some critical junctions and aborting when a preset limit
is exceeded? Integrand leaf counts may also be considered.

Integration Example #75 from Chapter 5 of the Timofeev Test Suite ran
into a 25-second timeout on Version 4.4. Does Rubi 4.5 resurface
eventually, and what is the final result, or error message?

I am curious how far Rubi 4.5 allows one to go with Martin's integrals:

<http://mathforum.org/kb/message.jspa?messageID=6477150&tstart=0>
<http://mathforum.org/kb/message.jspa?messageID=6872137&tstart=0>

Based on the analysis of an (incomplete) FriCAS computation, Waldek
Hebisch reported that the double integral is elementary only when
transformed to polar coordinates.

Martin.

© The Math Forum at NCTM 1994-2017. All Rights Reserved.