[Coin-discuss] OsiClpSolverInterface::modifyCoefficient problems

[James Gibbons]

Hi,

I'm having some problems with modifying matrix coefficients through the OsiClpSolverInterface, i.e. the modifyCoefficient member function. I'm reading in a LP file generated by Dash mosel, modifying the matrix and then resolving. Or at least that is my intention. There are two related problems

1. If I set keepZero to false, no coefficients are modifyemodified matrix. I'm writing a mixture of zeros and doubles. I've confirmed this by writing the matrix as an LP file after the attempted modification (it is the same as before) and by inserting some logging code in CoinPackedMatrix.cpp (no logging occurs). I've also tried getModelPtr()->modifyCoefficients with the same results. I'm also modifying some row and column bounds, this works fine.

2. If I set keepZero to true the matrix is modified (checked using the methods above) but now when presolving (using OsiPresolve) the matrix I get:

Assertion failed: nowUpper < large2, file CoinPresolveImpliedFree.cpp, line 306

However, I can load the modified matrix back into mosel and solve to the expected answers (with presolve) .

I guess I'm doing something wrong somewhere and would appreciate some pointers. My code is pretty complex and the problem large so it might be difficult to come up with a simple test case. However, I prepared to try if it would help,

Thanks,
James

-- 
Dr James Gibbons
Research Fellow
Division of Agricultural & Environmental Sciences
School of Biosciences
University of Nottingham
Sutton Bonington Campus
Loughborough
LE12 5RD

direct line: 0115 9516081
fax:           0115 9516060
e-mail:       james.gibbons at nottingham.ac.uk

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