On Sunday, April 24, 2016 at 12:04:27 AM UTC+1, Kiran Kedlaya wrote: > > On Saturday, April 23, 2016 at 3:36:28 PM UTC-7, Dima Pasechnik wrote: >> >> >> >> On Saturday, April 23, 2016 at 10:16:33 PM UTC+1, Kiran Kedlaya wrote: >>> >>> I just tried the following experiment on several different machines; >>> several different recent versions of Sage; algorithm = ple, m4ri; and n = >>> 20000, 25000, 30000. In all cases, the result is identical: >>> >>> sage: M = MatrixSpace(GF(2), n) >>> sage: for i in range(10): >>> ...: print M.random_element().rank() >>> 19937 >>> 19937 >>> 19937 >>> 19937 >>> 19937 >>> 19937 >>> 19937 >>> 19937 >>> 19937 >>> 19937 >>> >>> Using the Internet, I also retroactively tested this in Sage 4.0.1. >>> (Search in the page for "19937".) >>> >>> https://wiki.sagemath.org/sagebeatsmagma >>> >>> By contrast, I just tried a whole bunch of sparse examples coming from >>> Cremona modular symbols that gave more plausible answers, e.g.: >>> sage: S = CremonaModularSymbols(300001, sign=-1) >>> sage: T = >>> hecke_matrix(2).sage_matrix_over_ZZ().change_ring(GF(2)).dense_matrix() >>> sage: T.dimensions() >>> (27549, 27549) >>> sage: T.rank() >>> 27461 >>> >>> I'm not sure if this rank is correct, but at least it's not 19937. >>> >> >> well, this is hardly a surprise: >> >> sage: random_matrix? >> ... >> Warning: Matrices generated are not uniformly distributed. For >> unimodular matrices over finite field this function does not even >> generate all of them: for example "Matrix.random(GF(3), 2)" never >> generates "[[2,0],[0,2]]". This function is made for teaching >> purposes. >> >> Really? > > sage: l = [Matrix.random(GF(3),2) for i in range(10000)] > sage: len([i for i in l if i == 2]) > 114 > > The issue I raised appears to be distinct (see my response to Volker), but > maybe there should also be a ticket to correct this docstring. >
indeed, you have the codepath pointed out by Volker, not the one I kept in mind. Sorry for noise. Hope http://trac.sagemath.org/ticket/20493#comment:2 is useful. An entertaining bug! Dima -- 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 post to this group, send email to sage-devel@googlegroups.com. Visit this group at https://groups.google.com/group/sage-devel. For more options, visit https://groups.google.com/d/optout.
