[Symphony] Same version of symphony built with different -O options produces different solutions

[Peter Moceyunas]

Hi,

I have built symphony 5.4.0 on the same machine 5 different ways each 
using the same gcc compiler (3.4.4) but with different optimization 
flags: -g, -O0, -O1, -O2 and -O3.

I have models in which symphony produces different results across 1 or 
more of the different symphony executables.
I am guessing that this is occurring because of differences in floating 
point values due to the different register spills generated by the 
different optimization levels but not sure how to confirm this.

Further different compilers I have tried will generate different results 
- this is an issue as we would like our tool to produce the same result 
across linux and windows.

The models have a large number of constraints (20K-30K) and 
variables(10-30K) but typically solve fast (<few minutes) with no branching.
I believe all the coefficients in constraints and objective function of 
the LP are either 1 or -1

I can send examples if you are interested.

Any thoughts or suggestions ?

Pete