Dear Jesús,
The NEST Simulator documentation on parallel computing has a section regarding reproducibility:
https://nest-simulator.readthedocs.io/en/stable/hpc/parallel_computing.html
"To achieve the same simulation results even when using different parallelization strategies, the number of virtual processes has to be kept constant. A simulation with a specific number of virtual processes will always yield the same results, no matter how they are distributed over threads and processes, given that the seeds for the random number generators of the different virtual processes are the same (see Random numbers in NEST)."
Each virtual process has its own instance (and unique seed) in the random number generator. This will result in different typologies and random current/spikes generated. What you are describing is expected behavior.
Sincerely,
Wouter
On 26-Jul-23 12:10, Jesus Espinoza wrote:
Hello everyone,
I am writing to the NEST mailing list as I have encountered an issue in my simulation script, and I would greatly appreciate your insights.
The problem I am facing is that the membrane potential time course for a simulation with a fixed indegree seems to be dependent on the number of virtual processes (`total_num_virtual_procs`). Interestingly, this behavior does not occur for simulations with all-to-all connectivity.
The simulation involves a network with the following architecture: 5 `spike_generator` nodes connected to 5 `parrot_neuron` nodes with (all-to-all), which are further connected to 5 `iaf_psc_delta` neurons (all-to-all). The connections between the `iaf_psc_delta` neurons have an `fixed_indegree` of 2. A voltmeter is used to monitor the membrane potentials of these 5 neurons, and the simulation runs for 100 ms.
The issue arises when I vary the number of virtual processes (`total_num_virtual_procs`). I have tested the values 1, 2, and 4, and I have noticed that the plot of the membrane potentials at the end of the simulation differs for each `total_num_virtual_procs` value. Additionally, when I print the table of connections, I observe that the weights between the `iaf_psc_delta` neurons are also influenced by the number of virtual processes.
I have attached the simulation script and three images showing the plot for each `total_num_virtual_procs` value. The experiments were conducted on my personal Ubuntu machine.
The version of NEST that I am using is the latest at the time of writing this message, with commit `b9514cce789fb0b2c0dfbd9d0894d3986f743021`, authored by Abigail Morrison morrison@fz-juelich.de on Tue Jul 18 23:46:22 2023 +0200.
I would be grateful for any suggestions or explanations regarding this issue, as it hinders the reproducibility of my results.
Thank you in advance for your valuable help and support.
Best regards, Jesus Espinoza.
-- Jesús Espinoza Bergische Universität Wuppertal Fakultät für Mathematik und Naturwissenschaften Wissenschaftliches Rechnen und Hochleistungsrechnen Gaußstraße 20 42119 Wuppertal Germany E-Mail: espinozavalverd{at}uni-wuppertal.de
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