Hi Xavier,


The result of `GetConnections()` remains valid as long as no new synapses are added or synapses deleted, so in your case, you only need to call it once.

When you then do a `conn.weight`, you will get the weights at that point in time. But note that NEST only updates synaptic weights when a spike actually passes through the synapse, so you will get for each synapse the weight as it was at the end of the plasticity update when the most recent spike passed through that synapse.


Instead of calling Simulate() repeatedly, you can also use a RunManager context for higher efficiency, see https://nest-simulator.readthedocs.io/en/stable/nest_behavior/running_simulations.html#split-a-simulation-into-multiple-intervals.


In case you should be wondering why global instantaneous normalization is so cumbersome in NEST: We have focused on support for biologically plausible networks so far and instantaneous global normalization is just not biologically plausible (nor physically feasible with a view to causality).



Hans Ekkehard




Prof. Dr. Hans Ekkehard Plesser


Department of Data Science

Faculty of Science and Technology

Norwegian University of Life Sciences

PO Box 5003, 1432 Aas, Norway


Phone +47 6723 1560

Email hans.ekkehard.plesser@nmbu.no

Home http://arken.nmbu.no/~plesser




From: Xavier Otazu <xotazu@cvc.uab.cat>
Date: Thursday, 8 February 2024 at 19:46
To: users@nest-simulator.org <users@nest-simulator.org>
Subject: [NEST Users] Re: Weights assignment error with mpirun

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Hi Hans,

Thanks for your information. Fortunately, I do not normalize output connections (only input), hence, this code works for me.

Another question. Take that I call nest.Simulate() inside a for loop and I want to normalize weights after every iteration. In order to avoid calling GetConnections() for every loop iteration, may I get the connections calling GetConnections() just once? May I safely suppose that after every Simulate() new weights of my connections (they are changed because I use STDP) will be available (for reading) using the same variable? An example code would be something like:

my_conn = GetConnections(...)

for iter in range(...)
   normalize_connections(my_conn) # function that normalizes weights and calls nest.SetStatus(my_conn, ...)

Many thanks in advance!

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