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: Unrecogized expression for expansion". > > I saw a handful of TimeConstraineds 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...