Back to [[Releases]].

= Fast Downward 20.06 =

Fast Downward 20.06 was released on July 26, 2020.

Highlights:

 * The Singularity and Docker distributions of the planner now include LP support using the [[https://soplex.zib.de/|SoPlex]] solver out of the box. Thank you to ZIB for their solver and for giving permission to include it in the release.
   * !SoPlex is licensed under the [[https://scipopt.org/academic.txt|ZIB Academic License]].

 * The Vagrant distribution of the planner now includes LP support using the !SoPlex and/or CPLEX
 solvers out of the box if they are made available when the virtual machine is first provisioned. See
 QuickStart for more information.

 * A long-standing bug in the computation of derived predicates has
 been fixed. Thanks to everyone who provided bug reports for their
 help and for their patience!

 * A new and much faster method for computing stubborn sets has been
 added to the planner.

 * The deprecated merge strategy aliases `merge_linear` and `merge_dfp`
 have been removed.

== Downloads ==

 * source tarball: [[attachment:fast-downward-20.06.tar.gz||&do=get]]
 * Singularity container: [[https://www.singularity-hub.org/collections/3944|aibasel/downward:20.06 on Singularity Hub]]
 * Docker container: [[https://hub.docker.com/r/aibasel/downward|aibasel/downward:20.06 on Docker Hub]]
 * Vagrantfile: [[attachment:Vagrantfile||&do=get]] for Fast Downward 20.06

For Singularity, Docker and Vagrant, see QuickStart for instructions on how to run the planner. That page explains how to run the latest release of Fast Downward, so you have to amend the instructions if you want to run an older release.

For the tarball, if you have satisfied all dependencies, the following should build and run the planner with configuration alias `lama-first` on PDDL files `/path/to/domain.pddl` and `/path/to/problem.pddl` on a Linux or macOS system:
{{{#!bash
tar -xvzf fast-downward-20.06.tar.gz
cd fast-downward-20.06
./build.py
./fast-downward.py --alias lama-first /path/to/domain.pddl /path/to/problem.pddl
}}}

For dependencies and more advanced information (including Windows builds), see [[https://github.com/aibasel/downward/blob/main/BUILD.md|the build instructions]].

== Limitations ==

For licensing reasons, the binary distributions of Fast Downward have limited support for commercial LP solvers (CPLEX and Gurobi). The Docker and Singularity distributions only support !SoPlex. The Vagrant version supports !SoPlex and/or CPLEX if they are available at provisioning time. See QuickStart for more information.

== Referencing Fast Downward 20.06 ==

If you use this version of Fast Downward in a scientific publication, we encourage you to mention the version number, as in
"We ran experiments with Fast Downward 20.06." The canonical reference for citing Fast Downward is the following journal paper:

{{{
@Article{helmert-jair2006,
  author =  "Malte Helmert",
  title =   "The {Fast} {Downward} Planning System",
  journal = "Journal of Artificial Intelligence Research",
  year =    "2006",
  volume =  "26",
  pages =   "191--246"
}
}}}

== Changes in Fast Downward 20.06 ==

 * Fix crash of `--show-aliases` option of fast-downward.py.

 * Fix incorrect computation of derived predicates. <<BR>>
 http://issues.fast-downward.org/issue453 <<BR>>
 Derived predicates that were only needed in negated form and
 cyclically depended on other derived predicates could be computed
 incorrectly.

 * Integrate new pruning method `atom_centric_stubborn_sets` <<BR>>
 http://issues.fast-downward.org/issue781 <<BR>>
 We merged the code for the SoCS 2020 paper [[https://ai.dmi.unibas.ch/papers/roeger-et-al-socs2020.pdf|An Atom-Centric Perspective on Stubborn Sets"]].
 See [[Doc/PruningMethod]] for more information.

 * Remove deprecated merge strategy aliases `merge_linear` and `merge_dfp`. <<BR>>
 The deprecated merge strategy aliases `merge_linear` for linear
 merge strategies and `merge_dfp` for the DFP merge strategy are no longer
 available. See [[Doc/MergeStrategy]] for equivalent command line options to use these merge strategies.

 * For developers: use global logging mechanism for all output. <<BR>>
 http://issues.fast-downward.org/issue963 <<BR>>
 All output of the planner is now handled by a global logging mechanism, which
 prefaces printed lines with time and memory information. For developers, this
 means that output should no longer be passed to `cout` but to `utils::g_log`.
 Further changes to logging are in the works.

 * For developers: store enum options as enums (not ints) in Options objects. <<BR>>
 http://issues.fast-downward.org/issue962

 * For developers: allow creating Timers in stopped state. <<BR>>
 http://issues.fast-downward.org/issue965