[Scip] 70% of solving time is spent in checkLazyColArray

[Sebastian Ruther]

  Hello,

I noticed that a large amount of time is spent in checkLazyColArray. Of 
a time limit of 4h about 10k seconds (i.e. 70%) are spend in this 
function. Btw, this time is not accounted for in the output generated by 
SCIPprintStatistics.

The function has 2 double loops over nlazycols and ncols. When this 
function is called the first time, both are close to 40k. At that point 
the function takes 12 seconds to run. The function is called frequently 
when switching to a different node but not every time.

I assume that usually a larger number of columns can be handled by SCIP 
which would suggest that this function should not be called often as it 
is very expensive. So the question is: what can I do to avoid calling it?
Why does it shrink columns? Not sure if it has anything to do with it 
but I don't have colagelimit or cleanupcols(root) activated.

The call stack is
checkLazyColArray
SCIPlpShrinkCols
SCIPtreeLoadLP
SCIPconstructCurrentLP
solveNodeInitialLP
solveNodeLP
propAndSolve
solveNode
SCIPsolveCIP
SCIPsolve
runSCIP

FYI I'm still running SCIP 2.1.1

Thank you for your help,
Sebastian