Fast Downward 23.06 released

[Malte Helmert]

Dear Fast Downward group,

we are happy to announce the release of Fast Downward 23.06.


Highlights:

- The option parser of the search component has been completely
reimplemented. The new option parser has full error reporting where the
old code crashed on errors or silently accepted them. This is also an
important stepping stone towards a future use of Fast Downward as a
library. With the change, the --evaluator, --heuristic and --landmarks
options are now deprecated in favor of a new let syntax. For example,

--evaluator h=EVALUATOR --search SEARCH_ALGORITHM

is deprecated in favor of the expression

--search let(h, EVALUATOR, SEARCH_ALGORITHM)

- We now compile using the C++20 standard, so all modern C++ features
can be used as long as they are supported by all main compilers Fast
Downward supports (see README.md).

- The linear programming and mixed integer programming features of Fast
Downward now communicate directly with the LP/MIP solvers (SoPlex or
CPLEX) rather than using the open solver interface OSI as an
intermediary. This has also allowed us to move to more modern versions
of these solvers.

- The lmcount heuristic has been split into two separate heuristics
called landmark_sum and landmark_cost_partitioning. The former
corresponds to the old lmcount with the option admissible=false, the
latter to the old lmcount with the option admissible=true.

- The two new landmark heuristics (landmark_sum and
landmark_cost_partitioning) compute preferred operators more efficiently
than before. On average, this improves performance of LAMA-style planner
configurations.

- The merge-and-shrink heuristic now stores labels and their transitions
more efficiently, resulting in improved speed for merge-and-shrink
heuristic construction.

- The MIASM merge strategy for merge-and-shrink (more precisely, the
sf_miasm merge scoring function) now has an option to cache scores.
Caching is enabled by default and greatly speeds up construction of
MIASM-based merge-and-shrink heuristics.


To download the release and to see the full set of changes, see:

https://www.fast-downward.org/Releases/23.06

As always, please let us know if you encounter any problems with the
release artifacts (tarball, Apptainer image, Docker image, Vagrantfile).

Happy planning,
the Fast Downward team