[SCIP] presolve time

[Chuen Teck See]

Dear Scip,

1) I encountered a discrepancy in presolve time. I used 2 methods of timing. The first is using verblevel = 5. The second is to put a timing around SCIP_CALL( SCIPpresolve(scip) ). The result is as follows. (Observe the portion in Red)

original problem has 79800 variables (0 bin, 79800 int, 0 impl, 0 cont) and 159601 constraints
 159600 constraints of type <linear>
      1 constraints of type <SDP>
Reading Time: 0.71

solve problem
=============

transformed problem has 79800 variables (0 bin, 79800 int, 0 impl, 0 cont) and 159601 constraints
 159600 constraints of type <linear>
      1 constraints of type <SDP>

original problem has 239400 active (0.00187969%) nonzeros and 239400 (0.00187969%) check nonzeros

presolving:
(round 1, fast)       0 del vars, 159600 del conss, 0 add conss, 159600 chg bounds, 0 chg sides, 0 chg coeffs, 0 upgd conss, 0 impls, 0 clqs
clique table cleanup detected 0 bound changes

presolved problem has 79800 active (100%) nonzeros and 79800 (100%) check nonzeros

presolving (2 rounds: 2 fast, 1 medium, 1 exhaustive):
 0 deleted vars, 159600 deleted constraints, 0 added constraints, 159600 tightened bounds, 0 added holes, 0 changed sides, 0 changed coefficients
 0 implications, 0 cliques
presolved problem has 79800 variables (79800 bin, 0 int, 0 impl, 0 cont) and 1 constraints
      1 constraints of type <SDP>
transformed objective value is always integral (scale: 1)
Presolving Time: 0.25
SCIPpresolve(scip) time = 99.310370s

2) Also, I used >export OMP_NUM_THREADS=numCore & obtain the following. (My cpu has 6 core)
6 core: SCIPpresolve(scip) time = 124s
4 core: SCIPpresolve(scip) time = 115s
2 core: SCIPpresolve(scip) time = 93s
1 core: SCIPpresolve(scip) time = 749s

3) On a larger problem, 319600 variables (0 bin, 319600 int, 0 impl, 0 cont) and 639201 constraints, the time is very long
SCIPpresolve(scip) time on 2 core = 10538s

The scip I used is scipSdp (plugin developed by Tristan Gally). You can reproduce the behavior by compiling his plugin & I can provide the input file.


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