Re: [sage-support] Re: Making a copy of a MixedIntegerLinearProgram
OK I'll take a look :) On 15 May 2012 21:55, Nathann Cohen wrote: > Hell Emil !! > >> Any chance you could make a patch? :) (I'd volunteer myself, but I >> would probably mess it up!) > > H I could, but this patch is so local that it really is an > ideal occasion to write your first patch... Are you sure you do not > want to give it a try ? It is fun to be a developper, you will feel > like Sage becomes your home directory, and everybody will throw rocks > at you you create new bugs.. And all all the while you will be > having fun :-D > > Nathann > > -- > To post to this group, send email to sage-support@googlegroups.com > To unsubscribe from this group, send email to > sage-support+unsubscr...@googlegroups.com > For more options, visit this group at > http://groups.google.com/group/sage-support > URL: http://www.sagemath.org -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
Re: [sage-support] Re: Making a copy of a MixedIntegerLinearProgram
Hell Emil !! > Any chance you could make a patch? :) (I'd volunteer myself, but I > would probably mess it up!) H I could, but this patch is so local that it really is an ideal occasion to write your first patch... Are you sure you do not want to give it a try ? It is fun to be a developper, you will feel like Sage becomes your home directory, and everybody will throw rocks at you you create new bugs.. And all all the while you will be having fun :-D Nathann -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
Re: [sage-support] Re: Making a copy of a MixedIntegerLinearProgram
On 15 May 2012 15:21, Nathann Cohen wrote: > Oh, it's usually quite straightforward to implement such things. > Usually the feature already exists in the solver's C api, and all the > work that needs to be done is to expose it in Sage :-) Any chance you could make a patch? :) (I'd volunteer myself, but I would probably mess it up!) Emil -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
Re: [sage-support] Re: Making a copy of a MixedIntegerLinearProgram
Hellooo !! > Next issue is that the Gurobi backend doesn't support the copy: Oops ^^; > Any idea how much work this would be to do? Oh, it's usually quite straightforward to implement such things. Usually the feature already exists in the solver's C api, and all the work that needs to be done is to expose it in Sage :-) Nathann -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
Re: [sage-support] Re: Making a copy of a MixedIntegerLinearProgram
Next issue is that the Gurobi backend doesn't support the copy: AttributeError: 'sage.numerical.backends.gurobi_backend.GurobiBacke' object has no attribute 'copy' Any idea how much work this would be to do? (I can now do what I wanted to do before, at least with GLPK.) Emil -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
Re: [sage-support] Re: Making a copy of a MixedIntegerLinearProgram
On 15 May 2012 13:38, john_perry_usm wrote: >I've found MILP lets you do it this way: > > sage: x, y = lp[0], lp[1] Ahh! Thanks, this is what I need. (Is this documented anywhere?) - Emil -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
[sage-support] Re: Making a copy of a MixedIntegerLinearProgram
On Monday, May 14, 2012 7:32:25 PM UTC-5, Emil wrote: > > lp = MixedIntegerLinearProgram(maximization=True) > x = lp.new_variable() > > Then I do: > > nlp = copy(lp) > x = nlp.new_variable() > > The variable 'x' now seems to contain different variables. So I cannot > add any constraints that use the existing variables. Or is there some > way to do this? Thanks, > x *should* contain different variables, for two reasons. First, nlp already has a variable (a copy of the one you created for lp), so if you ask nlp to create a new variable for it, it won't return the variable lp created earlier. Second, after copying lp to nlp, you might want to change some variables in one from real to integer, or vice-versa. Also, I don't think Sage has ever let you create variables & add constraints that way. I don't know why, but if I want a variable with a compact notation, I've found MILP lets you do it this way: sage: x, y = lp[0], lp[1] but NOT sage: x, y = lp.new_variable(), lp.new_variable() You'll get variables alright, but you can't add constraints using the second. The first works fine. To add constraints, I usually do the following: sage: lp = MixedIntegerLinearProgram(maximization=False) sage: lp.add_constraint(2*lp[0] + 3*lp[1] <= 1) sage: nlp = copy(lp) sage: nlp.add_constraint(3*lp[0] - 2*lp[1] <= 1) Or, if you like, use x, y, etc., defining them as I did above (the FIRST way). regards john perry -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
Re: [sage-support] Re: Making a copy of a MixedIntegerLinearProgram
Hi Nathann, Thanks for writing the MILP class - it works very well. Now, I can do: x = lp.new_variable() Is there any way to do something like x = lp.get_existing_variables() ? I'm working on some graph theoretic stuff: I'm solving two LPs for each graph, for as many graphs as I can. - Emil. On 15 May 2012 08:00, Nathann Cohen wrote: > By the way, could I ask you what lead you to create and solve many LP ? I > mean, what are you solving which requires you to do that ? ^^; > > Nathann > > -- > To post to this group, send email to sage-support@googlegroups.com > To unsubscribe from this group, send email to > sage-support+unsubscr...@googlegroups.com > For more options, visit this group at > http://groups.google.com/group/sage-support > URL: http://www.sagemath.org -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
[sage-support] Re: Making a copy of a MixedIntegerLinearProgram
By the way, could I ask you what lead you to create and solve many LP ? I mean, what are you solving which requires you to do that ? ^^; Nathann -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
[sage-support] Re: Making a copy of a MixedIntegerLinearProgram
Hellooo Emil !!! Well, I just tried something and it ended upi crashing Sage, so I can just advise you to create all your variables in the first LP from the start, *then* to copy the MixedIntegerLinearProgram object. Of course it is a bad answer :-) John Perry was the one who needed this copy() feature for MILP and he was doing things similar to the ones you attempt. As I only had integer programs in mind when I wrote this class (hence hard problems to solve. hence the times it takes to generate the LP is totally small compared to the rest) I am totally ready to admit that it is not very suited to such computations. Dima mentionned recently that we may create some "LinearProgram" class at some point which would be thought *for* this type of problems, but I would fint it hard to write it myself considering that that would not be a user of it Hence no clue of what should be possible or not with it :-) Nathann -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
