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Re: [Bug-glpk] row deletion bug

From: Andrew Makhorin
Subject: Re: [Bug-glpk] row deletion bug
Date: Wed, 14 Feb 2007 16:34:24 +0300

> The row and column deletion does not work properly. The attached
> example shows 
> that the second solution could not be calculated with glpk. I debugged
> the 
> library and I found out that the row and the col "stat"s was not reset
> (so 
> the stat stayed LPX_BS) when I erase a row or col from the problem.
> And in
> the next lpx_warm_up one more or less basis will be in the matrix and
> it will 
> cause a failure in the library. Proper solution could be the resetting
> the 
> stats by the row/col type or the proper decreasing of the initial
> basis.

There is no bug. In your example you remove an active constraint,
so the basis becomes invalid.

If you want the basis to remain valid, you should not remove active
(non-basic) rows and basic columns. To attain that you could either
make the row non-active or just make it free, changing its bounds to
-inf and +inf and removing it when it becomes non-active.

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