[Coin-lpsolver] Getting tableau using getBInvARow or Col - notification
John J Forrest
jjforre at us.ibm.com
Thu Feb 10 15:57:55 EST 2005
Francois Margot found an inconsistency in the tableau routines of
Osi(Clp)SolverInterface. Given a constraint
x + y <= 8
the convention is to add a slack s so
x + y + s == 8 ( 0 <= s <= infinity)
and if the constraint is tight then the slack is at its lower bound. Clp
thinks in terms of row activities so the constraint looks like
x + y - s == 8 (-infinity <= s <= 0)
so if the constraint is tight the slack is at its upper bound.
I think I managed to fix the +1/-1 issue some months ago but I did not fix
the slack status inconsistency. I have now done that so that if other
solvers provide the tableau functionality then the status values should
match up. I do not expect this to affect many people but if you are
checking whether a slack is at its lower or upper bound by using something
like getBasisStatus then double-check your code still works.
John Forrest
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