On Mon, Mar 23, 2015 at 4:35 PM, Joachim Durchholz <[email protected]> wrote: > (Following up by myself) > > Background: The test does integrate(exp(-s*x)*sinh(x), (x, 0, oo)). > > Old sort order gives me > > Piecewise( > ( > -1/(s + 1)/2 - 1/(-s + 1)/2, #####1 > And( > Ne(1/s, 1), #####2 > Abs(periodic_argument(s, oo)) < pi/2, > Abs(periodic_argument(s, oo)) <= pi/2, > cos(Abs(periodic_argument(s, oo)))*Abs(s) - 1 > 0 > ) > ), > ( > Integral(exp(-s*x)*sinh(x), (x, 0, oo)), > True > ) > ) > > New sort order comes back with > Piecewise( > ( > -1/(2*(s + 1)) - 1/(2*(-s + 1)), #####1 > And( > Abs(periodic_argument(s, oo)) < pi/2, > Abs(periodic_argument(s, oo)) <= pi/2, > Ne(s, 1), ####2 > cos(Abs(periodic_argument(s, oo)))*Abs(s) - 1 > 0 > ) > ), > ( > Integral(exp(-s*x)*sinh(x), (x, 0, oo)), > True > ) > ) > > Points of interest: > > #####1 Different formulae, but same meaning. Haven't checked yet whether > that's just due to different term ordering or to different choices made > during Meijer. > > #####2 Now this is asserting Eq(1/s,1) for old and Eq(s,1) for new. These > are semantically different for the case s=0 (i.e. integral of just sinh(x)): > Old sort order gives a fail, new sort order gives a definite result. > Now I'm wondering how this is accidentally improving Meijer heuristics. (Or > is the difference mathematically irrelevant?) And I'm wondering where a > changed sort order might accidentally worsen the heuristics.
If s = 0 in either case Ne(s, 1) and Ne(1/s, 1) will be False, so I think in this case they are completely the same. The version with s is obviously simpler, but we shouldn't rely on the algorithm to give simple results, unless there are no other changes. I would try to find some other example that this gives different results for, or, preferably, get ahold of Tom Bachmann, and see if he can shed any insight. Aaron Meurer > > -- > You received this message because you are subscribed to the Google Groups > "sympy" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/sympy. > To view this discussion on the web visit > https://groups.google.com/d/msgid/sympy/55108726.2070803%40durchholz.org. > > For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "sympy" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/sympy. To view this discussion on the web visit https://groups.google.com/d/msgid/sympy/CAKgW%3D6JFNQnf%3D3sO6pZRSvKFx%2BumqFukg5TxRna8wTmxpGp2_w%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
