|Gromacs| 2019.4 release notes
------------------------------

This version was released on October 2nd, 2019. These release notes
document the changes that have taken place in |Gromacs| since the
previous 2019.3 version, to fix known issues. It also incorporates all
fixes made in version 2018.7 and earlier, which you can find described
in the :ref:`release-notes`.

.. Note to developers!
   Please use """"""" to underline the individual entries for fixed issues in the subfolders,
   otherwise the formatting on the webpage is messed up.
   Also, please use the syntax :issue:`number` to reference issues on GitLab, without the
   a space between the colon and number!

Fixes where mdrun could behave incorrectly
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Fix incorrect pressure when atoms in CMAP cross a box boundary
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

The virial calculation and thus the pressure would be incorrect
when the second and third atom involved in a CHARMM CMAP correction
term would reside in different periodic images. This can happen when
a protein is positioned over a box boundary. Note that the energy
and forces were correct, but sampling was affected when pressure
coupling was applied when a protein crossed a box boundary.

:issue:`2845`
:issue:`2867`

Fix incorrect LJ cut-off on GPU when rvdw < rcoulomb
""""""""""""""""""""""""""""""""""""""""""""""""""""

When rvdw was chosen by the user to be smaller than rcoulomb in the mdp file,
the LJ cut-off would initially be set to the Coulomb cut-off for computing
non-bonded interactions on the GPU. This only affected energy minimization,
mdrun -rerun and the first 2*nstlist steps of a normal MD run, since the correct
LJ cut-off is set when PME tuning (on by default) starts after 2*nstlist steps
(unless PME tuning was disabled with -notunepme).

:issue:`3056`


Fix (unlikely) missing bonded forces with CUDA GPUs and domain decomposition
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

Forces could be missing for bonded interactions computed on CUDA GPUs with
domain decomposition when there are non-local bonded interactions, but no
non-local non-bonded interactions between two domains. Note that this is
extremely unlikely to happen, since the distance between the bonded atoms
needs to be larger than the pair-list cut-off distance and there should be no
other non-local atoms within the pair-list cut-off distance.

:issue:`3063`

Fix incorrect reporting of final kinetic energy and temperature
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

With the leap-frog integrator, the kinetic energy and temperature reported
for the last step were incorrect when the last step was not divisible by
nstcalcenergy, nsttcouple or nstpcouple.

:issue:`2950`

Fix segmentation fault in grompp and mdrun with cosine COM pulling
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

:issue:`3023`


Fixes for ``gmx`` tools
^^^^^^^^^^^^^^^^^^^^^^^

Fix grompp not adding angle constraints between constraints
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

When using the mdp option constraints=all-angles, angles involving
bonds supplied as constraints in the topology would be removed,
but not replaced by angle constraints.

:issue:`3067`

Fix gmx wham with angle and dihedral geometries
"""""""""""""""""""""""""""""""""""""""""""""""

gmx wham would apply an incorrect radian to degree unit conversion,
leading to no overlap or not-a-number output.

:issue:`2609`
:issue:`3094`

Fix bug in gmx xpm2ps
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

The tool would fail when not being provided with a library file to read in.

:issue:`3012`

Fix bug in gmx anaeig
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

An issue was noted when reading a second set
set of eigenvectors that could lead to problems when the number
of eigenvectors was less than the three times the number of atoms.

:issue:`2972`

Fix issue with demux.pl script
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

The trajectories could become discontinuous with simulations longer than 100ns
and exchange strides that are not a multiple of 1 ps. This only affected the
post-processing of trajectories generated from replica exchange simulations.

Made gmx disre work with non-consecutively labeled restraints
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

:issue:`2953`

Fixed writing of gro files with index groups
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

An output ``.gro`` file from from e.g. ``gmx editconf -f -n`` would
take the atom names for the output file in order from the atoms in the
input file, rather than in order from the atoms indicated by the
indices in the index file.

:issue:`3107`

Made gmx make_ndx keep chain IDs
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

Old style structure file reading caused the chain IDs to be overwritten with
default values.

:issue:`3070`

Fixes that affect portability
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Disable PME OpenCL on Apple
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

The Apple OpenCL compilers fail to produce a functional clFFT build.
The OpenCL PME support is therefore disabled on Apple platforms.

:issue:`2941`

Miscellaneous
^^^^^^^^^^^^^

Added AMD Zen 2 detection
"""""""""""""""""""""""""

The AMD Zen 2 architecture is now detected as different from Zen 1
and uses 256-bit wide AVX2 SIMD instructions (GMX_SIMD=AVX2_256) by default. 
Also the non-bonded kernel parameters have been tuned for Zen 2.
This has a significant impact on performance.
