I am planning to organize sagespeciesdays for February, with making lazy power series sane as a subgoal. It would be extremely motivating if some people put themselves into the CC field of the ticket Frédéric pointed out, to signal interest.
Best wishes, Martin Frédéric Chapoton schrieb am Freitag, 11. Dezember 2020 um 11:03:59 UTC+1: > Salut, > Le code sur les espèces est connu pour être farci de bugs, et personne ne > s'en est préoccupé depuis très longtemps. > cf https://trac.sagemath.org/ticket/30727 > Fred > Le vendredi 11 décembre 2020 à 10:16:33 UTC+1, vivia...@gmail.com a > écrit : > >> Dear all, >> >> I discovered a weird bug on power series when computing the inverse of a >> serie. Look at this. >> >> This computation gives the expected result >> >> sage: L.<z> = LazyPowerSeriesRing(QQ) >> >> sage: f = 1 - z - z^2 >> >> sage: b = ~f >> >> sage: b.compute_coefficients(10) >> >> sage: b >> >> 1 + z + 2*z^2 + 3*z^3 + 5*z^4 + 8*z^5 + 13*z^6 + 21*z^7 + 34*z^8 + 55*z^9 >> + 89*z^10 + O(x^11) >> >> But not this one: >> >> sage: L.<z> = LazyPowerSeriesRing(QQ) >> >> sage: f = 1 - z - z^2 >> >> sage: f.compute_coefficients(10) >> >> sage: f >> >> 1 - z - z^2 + O(x^11) >> sage: b = ~f >> >> sage: b.compute_coefficients(10) >> >> sage: b >> >> 1 + z^1 + z^2 + z^3 + ... >> >> Another example with Catalan numbers >> >> sage: L.<z> = LazyPowerSeriesRing(QQ) >> sage: C = L() >> >> sage: C.define(1 + z*C*C) >> >> sage: Cinv = ~C >> >> sage: Cinv.compute_coefficients(10); Cinv >> >> 1 - z - z^2 - 2*z^3 - 5*z^4 - 14*z^5 - 42*z^6 - 132*z^7 - 429*z^8 - >> 1430*z^9 - 4862*z^10 + O(x^11) >> >> sage: C = L() >> >> sage: C.define(1 +z*C*C) >> >> sage: C.compute_coefficients(10);C >> >> 1 + z + 2*z^2 + 5*z^3 + 14*z^4 + 42*z^5 + 132*z^6 + 429*z^7 + 1430*z^8 + >> 4862*z^9 + 16796*z^10 + O(x^11) >> sage: Cinv = ~C >> >> sage: Cinv.compute_coefficients(10);Cinv >> >> 1 + z^1 + z^2 + z^3 + ... >> >> How Come?? >> >> This is Sage 9.2. I haven't tried on other versions >> >> -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/sage-devel/2dc78ece-15a9-4063-99fb-85fe4b4f3d35n%40googlegroups.com.
