as late as possible + total slack

[Ido Stein]

Hi,
when scheduling part of a project (several dependant F-S tasks) ALAP, i'm
receiving negative total slack only at the last task of the path. all other
tasks apears as TS=0.
when scheduling same path ASAP - negative slack appears to the whole path.

why? any ideas?

thanks in advance,
Ido.

 

[Jack Dahlgren]

Slack is determined using the formula Late finish - early finish. Obviously,
when tasks are as late as possible, their late finish and early finish are
identical. Therefore there is no negative slack, except for the last one.

While it would be nice to have a different algorithm for calculating slack
in this case I'm afraid you are stuck with what you have. I think that
putting in a must start on or start no earlier constraint would create
negative slack, in the same way that adding a finish constraint to an as soon
as possible schedule would work.

-Jack Dahlgren

 

[Ido Stein]

thanks Jack.
I guess i should leave the ALAP and work with SNET constraints.
Best regards,
Ido.