[Scip] Same SCIP, same ILP on different machines -> "different" results

[Gordon Royle]

I am running SCIP both on a Linux machine and a MacOS machine.

I am using the binaries

scip-2.0.2.darwin.x86_64.gnu.opt.spx
scip-2.0.2.linux.x86_64.gnu.opt.spx

When I run the same LP file (which is a binary pure integer linear program) on the two platforms, I get different computation paths and hence solve times. (One machine is faster than the other so a difference is expected there, but I did not expect different outcomes).

The values returned are correct - they are just different feasible solutions - but the variation can be quite large, which makes it different to perform comparative work.

Here are examples of the solve nodes for 12 ILPs of similar "type" - all have 273 variables and 274 constraints.

Each line has the format:  Nodes_on_mac ( Time_on_mac)  Nodes_on_linux ( Time_on_linux )

40 ( 5.00 )     40 ( 7.92 )
728 ( 7.55 )    1098 ( 13.24 )
10 ( 3.82 )     10 ( 5.79 )
96 ( 5.37 )     1298 ( 15.57 )
12008 ( 32.50 ) 887 ( 18.30 )
510 ( 6.79 )    648 ( 11.25 )
1560 ( 9.77 )   1418 ( 14.50 )
654573 ( 1200.07 )      223861 ( 663.25 )
28295 ( 65.48 ) 321577 ( 1033.71 )
28204 ( 63.66 ) 14652 ( 83.94 )
84891 ( 163.91 )        1752 ( 16.07 )
248229 ( 426.26 )       13963 ( 50.55 )

Why does this occur? Is it some sort of floating point issue or is there some arbitrariness in "tie-breaking" etc.

(I do not have a deep knowledge of the internal process of solving a pure ILP.)






Professor Gordon Royle
School of Mathematics and Statistics
University of Western Australia
Gordon.Royle at uwa.edu.au<mailto:Gordon.Royle at uwa.edu.au>













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