checking solution availability in OsiXprSolverInterface

[svigerske]

Issue created by migration from Trac.

Original creator: @pobonomo

Original creation time: 2006-06-27 14:56:46

Assignee: somebody

Version:

CC: @pobonomo

In OsiXprSolverInterface::getWarmStart, at the very beginning of the function line 321, there is a test which I think is invalid:

XPRS_CHECKED( XPRSgetintattrib, (prob_,XPRS_PRESOLVESTATE, &pstat) );
if ( pstat != 7 ) return NULL;

I guess that this is trying to test if the solution in Xpress is valid. If so, the bit 7 of pstat should be 1 (and not pstat==7) so the test should be:

if ( (pstat & 128) ==0 ) return NULL;

[svigerske]

Comment by @andrea5w created at 2006-08-13 22:03:03

Made suggested correction in branches/devel version

[svigerske]

Comment by @mjsaltzman created at 2006-10-28 23:46:49

pstat == 7 could also mean that the problem is loaded, LP presolved and MIP presolved, but the solution in memory is not valid.

Or it could be that what was intended is (pstat & 7) == 7, which would mean loaded, LP presolved, and MIP presolved, but validity is ignored.

There is another test like this on line 880. There are some other tests for whether presolve is done, but they are bitwise tests ((pstat & 6) == 0).

Unfortunately, this is code contributed by Dash. I will ask the author, but no promises that I can get an answer.

[svigerske]

Comment by @mjsaltzman created at 2006-10-28 23:46:49

Changing component from component1 to OsiXpr.

[svigerske]

Comment by @mjsaltzman created at 2006-10-28 23:48:37

Replying to [comment:2 mjs]:

Or it could be that what was intended is (pstat & 7) == 7, which would mean loaded, LP presolved, and MIP presolved, but validity is ignored.

Or even (pstat & 7) == 0 or (pstat & 7) != 0...

[svigerske]

Comment by @pobonomo created at 2006-11-30 06:15:26

Replying to [comment:3 mjs]:

Replying to [comment:2 mjs]:

Or it could be that what was intended is (pstat & 7) == 7, which would mean loaded, LP presolved, and MIP presolved, but validity is ignored.

Or even (pstat & 7) == 0 or (pstat & 7) != 0...

Sorry for not following up earlier.
The function tries to obtain a basis from XPRESS. I really don't see the relation between availability of a basis and the state of LP and MIP presolve.

In any case if there is no valid solution in memory I don't see how a basis is available.

I am not working with that anymore but when I tried to use this function a few months ago, I consistently obtained incorrect results.
Regards,
Pierre

[svigerske]

Comment by @mjsaltzman created at 2008-07-28 17:59:01

OK I am closing this. The patch has been in since at least r.951.

[svigerske]

Comment by @mjsaltzman created at 2008-07-28 17:59:01

Resolution: fixed