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[trivial] Add change log for version 24.06.
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(<https://issues.fast-downward.org>). Repository branches are named
after the corresponding tracker issues.

## Fast Downward 24.06

Released on October 10, 2024.

Highlights:

- We have improved the translator in several dimensions. Key
improvements include a revised and faster version of the invariant
algorithm, full support for negated predicates in the goal, and
improved error reporting for invalid PDDL. In addition, we have
moved the generation of negated axioms to the search component,
which can significantly improve the performance of configurations
that do not rely on negated axioms.

- We have implemented a new theory of landmark progression that, among
other things, closes a completeness gap for search configurations
like LAMA. Furthermore, this change makes it possible to use
reasonable orders for admissible landmark heuristics.

- We added the delete-relaxation operator-counting constraints
described by Masood Feyzbakhsh Rankooh and Jussi Rintanen.

- We have modernized the CMake build system, which now requires a
minimal version of CMake 3.16.

Details:

- bug fix: The planner now invokes destructors when terminating
(except for emergency situations where this is not possible) and
exits gracefully when running out of memory.
<https://issues.fast-downward.org/issue1138>
<https://issues.fast-downward.org/issue984>

- bug fix: Removed a dangling pointer in the state registry caused by
state copying.
<https://issues.fast-downward.org/issue1115>

- build: On M2 Macs it is now easier to build Fast Downward with CPLEX.

- build: We now support static linking of CPLEX.
<https://issues.fast-downward.org/issue1122>

- build: We modernized the CMake build system by updating the
requirement to CMake 3.16. New files must now be listed in
src/search/CMakeLists.txt for compilation. For Soplex support, users
need to set the soplex_DIR environment variable instead of
DOWNWARD_SOPLEX_ROOT. Futhermore, we renamed CMake options from
PLUGIN_FF_HEURISTIC_ENABLED to LIBRARY_FF_HEURISTIC_ENABLED.
<https://issues.fast-downward.org/issue1097>

- build: We added support for the `Validate` binary from newer VAL
versions, defaulting to `Validate` if `validate` is not found on the
PATH.
<https://issues.fast-downward.org/issue1123>

- build, for developers: We introduced the
`-Wzero-as-null-pointer-constant` flag to warn when 0 is used
instead of `nullptr` and the `-Wmissing-declarations` flag to detect
global functions not declared in header files, promoting static
declarations for visibility control.
<https://issues.fast-downward.org/issue1112>
<https://issues.fast-downward.org/issue1107>

- command line, for users: usage errors are now printed to stderr.
<https://issues.fast-downward.org/issue1084>

- command line, bug fix: Line breaks in command lines are now
correctly handled on Windows.
<https://issues.fast-downward.org/issue1120>

- driver: When running a portfolio, its component now prints the
absolute runtime as well as the relative runtime.
<https://issues.fast-downward.org/issue1131>

- driver: We have added the alias `seq-sat-fdss-2023` for the
satisficing Fast Downward Stone Soup 2023 portfolio.
<https://issues.fast-downward.org/issue1110>

- infrastructure: We have restructured the documentation for building
and running experiments. The build instructions are in the
[BUILD.md](BUILD.md) file. Developer-specific build information
has been moved to the "for developers" wiki section.
<https://issues.fast-downward.org/issue961>.

- infrastructure: We have removed the experiments directory from the
repository.
<https://issues.fast-downward.org/issue1116>

- infrastructure: We have updated the operating system versions and
software versions used for our GitHub actions test suite.
<https://issues.fast-downward.org/issue1142>

- landmarks, for users: We no longer break cycles in
landmark graphs because landmark progression can now deal
with cycles. Obedient-reasonable orderings are no longer used
because they had little impact on performance in our experiments
and they are not well-supported by theory.
<https://issues.fast-downward.org/issue996>
<https://issues.fast-downward.org/issue1089>

- landmarks, for users: Configurations with landmark heuristics are up
to 30% faster due to data structure optimizations.
<https://issues.fast-downward.org/issue1126>

- landmarks, for users: The landmark cost partitioning heuristic now
uses an enumeration to define the type of cost partitioning instead
of a Boolean. This affects the command line: `optimal={true,false}`
is now `cost_partitioning={optimal,uniform}`.
<https://issues.fast-downward.org/issue1091>

- landmarks, for developers: We updated variable, function, class and
file names within the landmark cost partitioning code.
<https://issues.fast-downward.org/issue1108>

- landmarks, for users: The algorithm for generating reasonable
landmark orderings is now deterministic and finds more orderings.
This has a positive impact on performance (number of
expansions, plan quality for satisficing configurations).
<https://issues.fast-downward.org/issue383>

- landmarks, for users: the landmark heuristics now consider an
operator preferred iff it achieves a landmark that is needed in the
future according to the heuristic. This replaces the previous, much
more convoluted definition.
<https://issues.fast-downward.org/issue1075>

- landmarks, bug fix: Landmark progression is now sound. The new
progression stores more information per state, leading to higher
memory requirements, but overall performance is only minimally
affected. With this change, it is now safe to use reasonable
orderings in the `landmark_cost_partitioning` heuristic. Since this
is in general beneficial, The `seq-opt-bjolp` alias now uses
reasonable orderings.
<https://issues.fast-downward.org/issue1036>

- landmarks, bug fix: We no longer wrongly assert that conjunctive
landmarks do not overlap with simple or disjunctive landmarks.
<https://issues.fast-downward.org/issue1087>

- LP/MIP solvers, bug fix: Empty constraint systems no longer lead to
crashes when using CPLEX.
<https://issues.fast-downward.org/issue1111>

- LP/MIP solvers, bug fix: We now call the correct methods of the LP
solvers for setting variable bounds.
<https://issues.fast-downward.org/issue1119>
<https://issues.fast-downward.org/issue1118>

- LP/MIP solvers, bug fix: CPLEX now compiles correctly on Windows for
arbitrary repository names.
<https://issues.fast-downward.org/issue1121>

- merge-and-shrink, for developers: We refactored and simplified the code
of the `merge_sccs` merge strategy.
<https://issues.fast-downward.org/issue1105>

- operator counting, for users: We implemented the delete-relaxation
operator-counting constraints described in "Efficient Computation and
Informative Estimation of h<sup>+</sup> by Integer and Linear
Programming" (Rankooh and Rintanen, ICAPS 2022).
For details, see
<https://www.fast-downward.org/Doc/ConstraintGenerator#Delete_relaxation_constraints_from_Rankooh_and_Rintanen>
<https://issues.fast-downward.org/issue1134>

- option parser, for users and developers: constructors no longer use
an encapsulated `Options` object, but take their parameters
directly. As a side effect, some command-line options now take their
parameters in a different order.
<https://issues.fast-downward.org/issue1082>

- option parser, for developers: We now support string arguments in
double quotes. Strings may use escape symbols `\"`, `\\`, and `\n`
for double quotes, backslashes and newlines.
<https://issues.fast-downward.org/issue1106>

- potential heuristics, bug fix: The potential optimizer now supports
effects that set a variable to a value that is already required by a
precondition. (The code will never generate such effects, but this
makes it possible to use task transformations that do generate such
effects.)
<https://issues.fast-downward.org/issue1150>

- search algorithms, bug fix: in the `eager` search algorithm, the
setting `reopen_closed=false` also affected open nodes, not just
closed nodes. This has now been fixed. Note that the previous
behavior did not affect the optimality of A* because it does not use
this setting.
<https://issues.fast-downward.org/issue1140>

- search algorithms, bug fix: Correctly propagate plan cost bounds to
components in iterated search in cases where manual cost bounds are
combined with bounds derived from incumbent solutions.
<https://issues.fast-downward.org/issue1130>

- translator and heuristics, for users: Negated axioms are now
computed in the search component and only for heuristics that need
them (relaxation heuristics, landmark heuristics, `cea` and `cg`).
This can lead to a large performance improvement for configurations
that do not use the aforementioned heuristics. We added a new option
for heuristics using negated axioms:

`axioms={approximate_negative,approximate_negative_cycles}`

`approximate_negative_cycles` is the old behavior and the new
default, while `approximate_negative` may result in less informative
heuristics, but avoids a potentially exponential number of negated
axioms.
<https://issues.fast-downward.org/issue454>

- translator, for users: We added full support for negative literals
in goals.
<https://issues.fast-downward.org/issue1127>

- translator: We removed a source of nondeterminism in the translator.
The translator should now be deterministic except for the effect of
the invariant synthesis timeout (option
`--invariant-generation-max-time`).
<https://issues.fast-downward.org/issue879>

- translator, for users: We improved error reporting for invalid PDDL
input.
<https://issues.fast-downward.org/issue1030>

- translator, bug fix: Uninitialized numeric expressions are now
handled correctly by the translator.
<https://issues.fast-downward.org/issue913>

- translator, bug fix: There was a conceptual gap in the invariant
synthesis algorithm. This has been fixed by a revised algorithm,
which is also faster.
<https://issues.fast-downward.org/issue1133>

## Fast Downward 23.06

Released on July 31, 2023.
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