In this cell, I have a linear programming problem: http://sagecell.sagemath.org/?q=oatgsd
However, the answer is wrong. The optimal objective has to be 1 whereas it is 0. The optimal values for x and y lie on the line between (-2,1) and (1,-2). I have shown the values of the constraints for the point (-1,0)
Helloooooooooooooooooooooo !!
That's because all variables are assumed to be >= 0 by default unless specified otherwise. Sorry for that, it's something that all LP solvers that I know assume too (and that's why we do, too), and it's pretty hard to advertise in the doc and make sure that everybody sees it O_o
So if you want to make this work with negative values, you have to add lines like :
p.set_min(p['x'],None)
p.set_min(p['y'],None)
in your code. And it will work, at least it does on my computer.
Perhaps I should add warnings everywhere in the doc O_o
Nathann
Well, the doc mentions it since 12332. But printing stuff in the doc is not always enough, especially when the LP above does not even call new_variable :-/ I created http://trac.sagemath.org/ticket/15482 to make it more visible.
Asked: 2013-12-03 21:22:48 +0200
Seen: 295 times
Last updated: Dec 04 '13
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I'm baffled here. The only suggestion I have is that somehow it doesn't like maximizing functions that have many negative values - I get similar problems with anything negative for coefficients.