Concurrent action plans

[Siggi]

Hey everybody

Is there any way to have fast-downward find plans that have concurrent non-interfering actions (more than one action per time step of the plan)?

Thanks

-Siggi

[Malte Helmert]

Not directly; the planner is purely sequential.

One way to generate a parallel plan is to first find a sequential plan
with a sequential planner like Fast Downward, then schedule it into a
parallel plan in a post-processing step with another tool. For example,
Patrik Haslum's pddlcat tool has a mode for scheduling sequential plans
into parallel ones (see
http://users.cecs.anu.edu.au/~patrik/un-hsps.html for the code; you will
probably have to ask Patrik for how to do this scheduling, since pddlcat
has zillions of options).

One problem with that setup is that if you want to minimize something
like number ot time steps, the sequential planner used in the first
stage won't be aware of that (it will attempt to minimize total action
cost instead), and hence it won't actively search for plans that
parallelize well. If that is a problem in your domain, it may be worth
restating the domain as a temporal planning domain and use a temporal
planner (such as LPG-TD or Temporal Fast Downward). Temporal planners
tend to scale somewhat worse than sequential ones, but should produce
higher-quality plans.

Cheers,

Malte