Hi Matt, There is indeed a bug in GAP, to do with downward running ranges. I believe this can be fixed by adding the following lines to the start of the 'JoinRanges' method (which is at line 2538 of file lib/coll.gi on my machine), but not this fix is not completely tested yet.
# Make ranges run upwards if da < 0 then x:=a1;a1:=a0;a0:=x;da:=-da; fi; if db < 0 then x:=b1;b1:=b0;b0:=x;db:=-db; fi; I am currently testing this fix carefully, and making sure there are no similar bugs. Chris On 05/12/2014 21:58, "Matt Fayers" <m.fay...@qmul.ac.uk> wrote: >Dear GAP forum, > >I am experiencing some strange behaviour with GAP's Union function: the >command > >Union([2],[3],[5,1..1]); > >returns > >[2,3] > >rather than the expected [1,2,3,5]. (If I do > >Union([2],[3],[5,1]) > >or > >Union([2],[5,1..1]) > >the behaviour is as expected.) > >Any ideas? I'm running GAP 4.7.5 on Linux (because that's the version >that comes with my Linux distribution); I apologise if this has already >been resolved in a more recent version. > >Best wishes, >Matt Fayers. >____________________________________________________________________ > >Matthew Fayers >School of Mathematical Sciences >Queen Mary University of London >Mile End Road >London >E1 4NS >020 7882 5479 >www.maths.qmul.ac.uk.~mf/ >____________________________________________________________________ > >_______________________________________________ >Forum mailing list >Forum@mail.gap-system.org >http://mail.gap-system.org/mailman/listinfo/forum _______________________________________________ Forum mailing list Forum@mail.gap-system.org http://mail.gap-system.org/mailman/listinfo/forum
