[Clp] Question about ClpPrimalColumnPivot.saveWeights

[John Forrest]

Documentation?

Setting model_ may be necessary on more than one mode call - so just 
laziness and with computers/compilers may not cost anything.

saveWeights is only useful with steepest edge (which is default).  For 
badly behaved problems the code may factorize the problem and find the 
basis is singular.  In that case it throws away the iterations since the 
previous factorization and reduces the number of iterations between 
factorizations.  So when it throws away pivots, it needs to go back to 
the weights which were correct at previous factorization.

John Forrest

On 11/09/2020 06:24, Dami Choi wrote:
> Hello,
> 
> I hope this isn't a stupid question, but I felt like I didn't understand 
> the documentation.
> What is the purpose of the saveWeights function in ClpPrimalColumnPivot?
> I'm also confused why the model_ attribute has to be reset everytime the 
> saveWeights is called, for example here 
> <https://projects.coin-or.org/Clp/browser/trunk/src/ClpPrimalColumnDantzig.hpp#L41> 
> and here 
> <https://projects.coin-or.org/Clp/browser/trunk/src/ClpPrimalColumnSteepest.cpp#L3168>. 
> What is the reason for this? If primal() is called from ClpSimplex, then 
> doesn't the model always result in the same model? Why update this every 
> time?
> 
> Thank you,
> 
> Dami
> 
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