Sampling of quantum properties is performed via the so-called classical isomorphism of path integral. In this scheme , a quantum degree of freedom is mapped into a classical polymer with a certain number of beads. This number of beads increases with the relevance of quantum effects and can become very large. Because in the sampling procedure, generally, for each polymer bead a potential energy evaluation is required within a single sampling step, polymer sampling subroutines become a bottleneck. Openmpbeads is a patch to the PaPIM code which increases the code’s performance by parallelizing the polymer chain sampling subroutines. The module introduces the OpenMP parallelization loops for the polymer sampling subroutines. In this way, a considerable increase of performance can be achieved.
The PaPIM program source code (for PaPIM download see here) and Git should be available. The downloaded Openmpbeads patch should be placed in the PaPIM main directory, and applied to the PaPIM source code by executing the following command:
git apply openmpbeads.patch
After the patch has been successfully applied, the OpenMP parallelized PaPIM code can be re-compiled as described in the PaPIM documentation.
The successful Openmpbeads patch application and compilation should be verified by executing the
codes standard tests.
The code’s tests are located in the directory
The same set of tests as for the verification of the PaPIM code is executed, but now
with the addition of utilizing OpenMP parallelization. Thus a number of processor cores available for the test
should be at least two.
For details of the PaPIM code standard tests see here.
Before running the tests the code has to be properly compiled by running the
make command in the
./source sub-directory (see compilation of PaPIM code here).
numdiff package is used for automatic comparison purposes and should be made available before running the tests,
diff command will be used automatically instead but the user is warned that the test might fail
due to small numerical differences.
The tests are performed automatically by executing the following command in the
cd tests ./test.sh -m [number of MPI cores] -o [number of OpenMP cores]
[number of MPI cores] should not exceed 20, and the
[number of OpenMP cores] should not exceed 5.
The product of
[number of MPI cores] and
[number of OpenMP cores] should not exceed to the total number
of available cores on the system and should also not exceed number 100.
Due to small numerical discrepancies between generated outputs and reference values which can cause the tests to fail,
the user is advised to manually examine the numerical differences between generated output and the corresponding
reference values in case the tests fail.
The Openmpbeads module patch is located at: https://gitlab.e-cam2020.eu/Quantum-Dynamics/PIM/tree/openmpbeads.