<br><font size=2 face="sans-serif">James,</font>
<br>
<br><font size=2 face="sans-serif">Seems like you have hit two separate
bugs. I would guess the second one is a bug in OsiPresolve. It
looks as if ClpPresolve gets rid of zero elements before doing main part
of presolve. What happens if you don't do OsiPresolve but just call
OsiClpSolverInterface::initialSolve() - it should do a ClpPresolve and
so should be OK? I will see if you have given enough information
for me to track down first bug. I will try to have that fixed by
Monday. If I have the time and energy I may move a function - allElementsInRange
from ClpPackedMatrix to CoinPackedMatrix and then it will be easy to modify
OsiPresolve.</font>
<br>
<br>
<br><font size=2 face="sans-serif">John Forrest</font>
<br>
<br>
<br>
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<td width=40%><font size=1 face="sans-serif"><b>"James Gibbons"
<James.Gibbons@nottingham.ac.uk></b> </font>
<br><font size=1 face="sans-serif">Sent by: coin-discuss-bounces@list.coin-or.org</font>
<p><font size=1 face="sans-serif">03/23/2006 01:10 PM</font>
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<div align=center><font size=1 face="sans-serif">Please respond to<br>
Discussions about open source software for Operations Research
<coin-discuss@list.coin-or.org></font></div></table>
<br>
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<td>
<div align=right><font size=1 face="sans-serif">To</font></div>
<td><font size=1 face="sans-serif"><coin-discuss@list.coin-or.org></font>
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<td>
<div align=right><font size=1 face="sans-serif">cc</font></div>
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<td>
<div align=right><font size=1 face="sans-serif">Subject</font></div>
<td><font size=1 face="sans-serif">[Coin-discuss] OsiClpSolverInterface::modifyCoefficient
problems</font></table>
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<br><tt><font size=2>Hi,<br>
<br>
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<br>
<br>
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.<br>
<br>
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:<br>
<br>
Assertion failed: nowUpper < large2, file CoinPresolveImpliedFree.cpp,
line 306<br>
<br>
However, I can load the modified matrix back into mosel and solve to the
expected answers (with presolve) .<br>
<br>
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,<br>
<br>
Thanks,<br>
James<br>
<br>
-- <br>
Dr James Gibbons<br>
Research Fellow<br>
Division of Agricultural & Environmental Sciences<br>
School of Biosciences<br>
University of Nottingham<br>
Sutton Bonington Campus<br>
Loughborough<br>
LE12 5RD<br>
<br>
direct line: 0115 9516081<br>
fax: 0115 9516060<br>
e-mail: james.gibbons@nottingham.ac.uk<br>
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