Dear Johan,


You do not tell us what the “result” number is that you print out. But I notice that the value you get when running with 10 MPI processes on PDC, is about 10 times smaller than the value you see with one process on your PC.


I’ll venture a guess and assume you have a network of N neurons which you connect to one spike detector. You simulate, read out the number of spikes and convert it into a firing rate, dividing number of spikes by N * simtime.


In an MPI-parallel simulation, the spike detector on each MPI process only gets the spikes of neurons simulated on that MPI process. If you still divide by the full number of neurons to compute the rate, one would expect exactly the behavior you observe.


In the future, please provide more details about what you are doing, so we can provide more pointed advice.



Hans Ekkehard




Prof. Dr. Hans Ekkehard Plesser

Head, Department of Data Science


Faculty of Science and Technology

Norwegian University of Life Sciences

PO Box 5003, 1432 Aas, Norway


Phone +47 6723 1560





On 19/02/2021, 22:20, "JOHAN LILJEFORS" <> wrote:


Dear Nest users,

I am fairly new to Nest having used it only for a few months and it has been working without any problems on my PC running Linux. Recently I was given access to a PDC  where I have been submitting jobs but I am encountering a problem with my model. I'm running Python 3.7.3 and Nest 2.18.


On both my PC and on the PDC, I run the following python script:


import Nest


For counter in range(0,10):





I execute this with "srun -n=1 python3"

This outputs 10 numbers, ranging from 0.35-0.4.


On the PDC, i run the same scripts but without the for loop:


import Nest






I execute this with "srun -n=10 python3"

this outputs 10 numbers, but this time much smaller around 0.04. 


I am not doing any file operations, nor any MPI communication between the tasks and I am genuinely confused as to how submitting multiple tasks can yield a different result than a single task.


Has anyone encountered anything similar?


Johan Liljefors