Saturday, May 24, 2008

GAMS/Cplex bug: iteration count reported as zero

In some cases GAMS/Cplex reports erroneously that zero iterations have been performed. Example: run THAI model from the model library with iterlim=5:

S O L V E S U M M A R Y

MODEL thainavy OBJECTIVE obj
TYPE MIP DIRECTION MINIMIZE
SOLVER CPLEX FROM LINE 84

**** SOLVER STATUS 4 TERMINATED BY SOLVER
**** MODEL STATUS 14 NO SOLUTION RETURNED
**** OBJECTIVE VALUE 0.0000

RESOURCE USAGE, LIMIT 0.037 1000.000
ITERATION COUNT, LIMIT 0 5

The SOLVER STATUS is also wrong, this should be 2 ITERATION INTERRUPT. Turns out I have reported this already in january 2006, but it does not seem to get fixed.

Correct values for these settings are often important when running Cplex from a more complex algorithm formulated in GAMS.