The following GAMS code was very slow:
ACCRLRLY(B,BA,Y,U)$SUM((H,T,UR), XSB7(B,BA,"NP",H,Y,T,U,UR)) |
Note that the $ condition on the left is correct: it makes sure we don’t take the SMAX of an empty set. This is really needed as SMAX over an empty set is unreliable (see:http://yetanothermathprogrammingconsultant.blogspot.com/2008/05/gams-smin-bug.html).
However the SMAX will not skip zeros like a SUM, making this operation very slow. A possible fix is:
| ACCRLRLY(B,BA,Y,U)$SUM((H,T,UR), XSB7(B,BA,"NP",H,Y,T,U,UR)) = ACRLRLY(BA,Y, U) * SMAX((H,T,UR)$XSB7(B,BA,"NP",H,Y,T,U,UR), XSB7(B,BA,"NP",H,Y,T,U,UR)); |
The difference in timing is very large:
| Original | 75 seconds |
| New version | 0.9 seconds |
This only works if it is safe to skip zeros. I.e. if there are positive elements in each smax. We can check for this e.g. by using an abort$(cond) statement.