Hi Hans!

About first point, I agree it appears risky, but users of this function are aware of what it implies. If somebody doesn't want to take this risk, a GetNodeCollection() function is OK.

About second point, I do not use GetLocalNodeCollection() with devices (do not know about other users). As said before, if it is explained in the function documentation, the user should take the risk of using it.

About third point ... I take the local nodes in order to retrieve the incoming synapsis weights (hence, these variables are also "local" for every MPI process). I perform weight normalization (there is an example in the web documentation page) and it is MUCH faster when performed on local nodes (every MPI automatically processes ONLY its own weights). I also change nodes parameters, but it is not a bottleneck. But if you say that from version 3.10 GetLocalNodeCollection() is slower and, in addition, it does not work correctly with spatial node collections (I use them), then I have a serious problem ... 🙁

Best,

Xavier

From: Hans Ekkehard Plesser <hans.ekkehard.plesser@nmbu.no>
Sent: Friday, June 12, 2026 11:40 AM
To: NEST User Mailing List <users@nest-simulator.org>
Subject: [NEST Users] Re: GetLocalNodeCollection at version 3.10

Hello Xavier,

Thank you very much for your input! We deprecated GetLocalNodeCollection() for several reasons:

MPI-rank specific operations at the Python-level appear inherently risky. Ideally, the Python level should work on the entire network and the C++ kernel below ensure that the operations are correctly executed on the ranks.
In all versions up to 3.9, it would not work correctly when used on collections containing devices, such as poisson generators or spike recorders. See https://github.com/nest/nest-simulator/pull/3632 for details.
In 3.10, it works correctly now in all cases, but is considerably slower and does not work properly with spatial node collections. See https://github.com/nest/nest-simulator/issues/3706 for a discussion.

But it may be that we have overlooked important use cases for doing rank-specific operations based on GetLocalNodeCollection(). Could you write a bit about your use case?

Best,

Hans Ekkehard

Prof. Dr. Hans Ekkehard Plesser

Research Committee Chair, Faculty of Science and Technology

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: Friday, 12 June 2026 at 10:40
To: users@nest-simulator.org <users@nest-simulator.org>
Subject: [NEST Users] GetLocalNodeCollection at version 3.10

Hi!

I have seen that in the latest 3.10 version you have deprecated GetLocalNodeCollection() ...

I would very please you to DON'T do it. Since it has the "Local" word, we users know that it only returns MPI nodes. Hence, we know that we have to deal with it and the hight risk of incorrect code, but it is not more difficult that writing concurrent code in mind. This function HUGELY accelerates execution of the code because we (programmers) know that it (and operations on nodes and their connections) is executed in different MPI processes with different data.

Best,

Xavier
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