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
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.nomailto: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 _______________________________________________ NEST Users mailing list -- users@nest-simulator.org To unsubscribe send an email to users-leave@nest-simulator.org
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.nomailto: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 _______________________________________________ NEST Users mailing list -- users@nest-simulator.org To unsubscribe send an email to users-leave@nest-simulator.org
Computer Vision Centerhttp://www.cvc.uab.cat CONFIDENTIALITY WARNINGhttp://www.cvc.uab.es/?page_id=7475
Hi Xavier,
I find your observation slightly surprising. I assume you do very roughly something like this:
n = nest.Create(...) nest.Connect(n, n) l = nest.GetLocalNodeCollection(n) c = nest.GetConnections(source=n, target=l) w = c.weight total_w = sum(w) # and sum across MPI processes c.weight /= total_w
The critical point here being the GetConnections() call. Since GetConnections() only returns connections with local targets, the following two calls should give identical results:
nest.GetConnections(source=n, target=l) nest.GetConnections(source=n, target=n)
I haven't had time to look at the implementation of GetConnections() yet, but naïvely I'd almost expect the first call to be slower, because the node collection l has a more complicated structure than the node collection n.
If my interpretation of your use case is correct, we should take a look at the implementation of GetConnections().
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.nomailto:hans.ekkehard.plesser@nmbu.no Home http://arken.nmbu.no/~plesser From: Xavier Otazu Porter xotazu@cvc.uab.cat Date: Monday, 15 June 2026 at 11:37 To: NEST User Mailing List users@nest-simulator.org Subject: [NEST Users] Re: GetLocalNodeCollection at version 3.10
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.nomailto: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 _______________________________________________ NEST Users mailing list -- users@nest-simulator.org To unsubscribe send an email to users-leave@nest-simulator.org
Computer Vision Centerhttp://www.cvc.uab.cat CONFIDENTIALITY WARNINGhttp://www.cvc.uab.es/?page_id=7475
Hi Hans,
Yes, I have something similar to this.
From the moment I used the GetLocalNodeCollection() function, everything is much faster. I guess it is the for loop needed to go through all the neurons (I need a for loop because I have an array pointing to every neuron).
Xavier
________________________________ From: Hans Ekkehard Plesser hans.ekkehard.plesser@nmbu.no Sent: Monday, June 15, 2026 2:53 PM To: NEST User Mailing List users@nest-simulator.org Subject: [NEST Users] Re: GetLocalNodeCollection at version 3.10
Hi Xavier,
I find your observation slightly surprising. I assume you do very roughly something like this:
n = nest.Create(...) nest.Connect(n, n) l = nest.GetLocalNodeCollection(n) c = nest.GetConnections(source=n, target=l) w = c.weight total_w = sum(w) # and sum across MPI processes c.weight /= total_w
The critical point here being the GetConnections() call. Since GetConnections() only returns connections with local targets, the following two calls should give identical results:
nest.GetConnections(source=n, target=l) nest.GetConnections(source=n, target=n)
I haven't had time to look at the implementation of GetConnections() yet, but naïvely I'd almost expect the first call to be slower, because the node collection l has a more complicated structure than the node collection n.
If my interpretation of your use case is correct, we should take a look at the implementation of GetConnections().
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.nomailto:hans.ekkehard.plesser@nmbu.no Home http://arken.nmbu.no/~plesser From: Xavier Otazu Porter xotazu@cvc.uab.cat Date: Monday, 15 June 2026 at 11:37 To: NEST User Mailing List users@nest-simulator.org Subject: [NEST Users] Re: GetLocalNodeCollection at version 3.10
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.nomailto: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 _______________________________________________ NEST Users mailing list -- users@nest-simulator.org To unsubscribe send an email to users-leave@nest-simulator.org
Computer Vision Centerhttp://www.cvc.uab.cat CONFIDENTIALITY WARNINGhttp://www.cvc.uab.es/?page_id=7475
Computer Vision Centerhttp://www.cvc.uab.cat CONFIDENTIALITY WARNINGhttp://www.cvc.uab.es/?page_id=7475
Sorry for this second message ...
I do the calls to GetLocalNodeCollection() and GetConnections() (the first 5 lines of your example) only one time (at the beginning of my program).
For every iteration (I change poisson_generators rate every few miliseconds) I perform the weight normalization (the variables already point to the weights). That is, the two last lines of your example are much faster when I use GetLocalNodeCollection().
Xavier
________________________________ From: Xavier Otazu Porter xotazu@cvc.uab.cat Sent: Monday, June 15, 2026 3:09 PM To: NEST User Mailing List users@nest-simulator.org Subject: [NEST Users] Re: GetLocalNodeCollection at version 3.10
Hi Hans,
Yes, I have something similar to this.
From the moment I used the GetLocalNodeCollection() function, everything is much faster. I guess it is the for loop needed to go through all the neurons (I need a for loop because I have an array pointing to every neuron).
Xavier
________________________________ From: Hans Ekkehard Plesser hans.ekkehard.plesser@nmbu.no Sent: Monday, June 15, 2026 2:53 PM To: NEST User Mailing List users@nest-simulator.org Subject: [NEST Users] Re: GetLocalNodeCollection at version 3.10
Hi Xavier,
I find your observation slightly surprising. I assume you do very roughly something like this:
n = nest.Create(...) nest.Connect(n, n) l = nest.GetLocalNodeCollection(n) c = nest.GetConnections(source=n, target=l) w = c.weight total_w = sum(w) # and sum across MPI processes c.weight /= total_w
The critical point here being the GetConnections() call. Since GetConnections() only returns connections with local targets, the following two calls should give identical results:
nest.GetConnections(source=n, target=l) nest.GetConnections(source=n, target=n)
I haven't had time to look at the implementation of GetConnections() yet, but naïvely I'd almost expect the first call to be slower, because the node collection l has a more complicated structure than the node collection n.
If my interpretation of your use case is correct, we should take a look at the implementation of GetConnections().
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.nomailto:hans.ekkehard.plesser@nmbu.no Home http://arken.nmbu.no/~plesser From: Xavier Otazu Porter xotazu@cvc.uab.cat Date: Monday, 15 June 2026 at 11:37 To: NEST User Mailing List users@nest-simulator.org Subject: [NEST Users] Re: GetLocalNodeCollection at version 3.10
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.nomailto: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 _______________________________________________ NEST Users mailing list -- users@nest-simulator.org To unsubscribe send an email to users-leave@nest-simulator.org
Computer Vision Centerhttp://www.cvc.uab.cat CONFIDENTIALITY WARNINGhttp://www.cvc.uab.es/?page_id=7475
Computer Vision Centerhttp://www.cvc.uab.cat CONFIDENTIALITY WARNINGhttp://www.cvc.uab.es/?page_id=7475
Computer Vision Centerhttp://www.cvc.uab.cat CONFIDENTIALITY WARNINGhttp://www.cvc.uab.es/?page_id=7475
Hello Xavier,
Could you share an actual reproducer? If you don't want to post it to the mailing list here, you can also send it to me directly (do not use .py as suffix for technical reasons, archives are fine).
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.nomailto:hans.ekkehard.plesser@nmbu.no Home http://arken.nmbu.no/~plesser From: Xavier Otazu Porter xotazu@cvc.uab.cat Date: Monday, 15 June 2026 at 15:17 To: NEST User Mailing List users@nest-simulator.org Subject: [NEST Users] Re: GetLocalNodeCollection at version 3.10
Sorry for this second message ...
I do the calls to GetLocalNodeCollection() and GetConnections() (the first 5 lines of your example) only one time (at the beginning of my program).
For every iteration (I change poisson_generators rate every few miliseconds) I perform the weight normalization (the variables already point to the weights). That is, the two last lines of your example are much faster when I use GetLocalNodeCollection().
Xavier
________________________________ From: Xavier Otazu Porter xotazu@cvc.uab.cat Sent: Monday, June 15, 2026 3:09 PM To: NEST User Mailing List users@nest-simulator.org Subject: [NEST Users] Re: GetLocalNodeCollection at version 3.10
Hi Hans,
Yes, I have something similar to this.
From the moment I used the GetLocalNodeCollection() function, everything is much faster. I guess it is the for loop needed to go through all the neurons (I need a for loop because I have an array pointing to every neuron).
Xavier
________________________________ From: Hans Ekkehard Plesser hans.ekkehard.plesser@nmbu.no Sent: Monday, June 15, 2026 2:53 PM To: NEST User Mailing List users@nest-simulator.org Subject: [NEST Users] Re: GetLocalNodeCollection at version 3.10
Hi Xavier,
I find your observation slightly surprising. I assume you do very roughly something like this:
n = nest.Create(...) nest.Connect(n, n) l = nest.GetLocalNodeCollection(n) c = nest.GetConnections(source=n, target=l) w = c.weight total_w = sum(w) # and sum across MPI processes c.weight /= total_w
The critical point here being the GetConnections() call. Since GetConnections() only returns connections with local targets, the following two calls should give identical results:
nest.GetConnections(source=n, target=l) nest.GetConnections(source=n, target=n)
I haven't had time to look at the implementation of GetConnections() yet, but naïvely I'd almost expect the first call to be slower, because the node collection l has a more complicated structure than the node collection n.
If my interpretation of your use case is correct, we should take a look at the implementation of GetConnections().
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.nomailto:hans.ekkehard.plesser@nmbu.no Home http://arken.nmbu.no/~plesser From: Xavier Otazu Porter xotazu@cvc.uab.cat Date: Monday, 15 June 2026 at 11:37 To: NEST User Mailing List users@nest-simulator.org Subject: [NEST Users] Re: GetLocalNodeCollection at version 3.10
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.nomailto: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 _______________________________________________ NEST Users mailing list -- users@nest-simulator.org To unsubscribe send an email to users-leave@nest-simulator.org
Computer Vision Centerhttp://www.cvc.uab.cat CONFIDENTIALITY WARNINGhttp://www.cvc.uab.es/?page_id=7475
Computer Vision Centerhttp://www.cvc.uab.cat CONFIDENTIALITY WARNINGhttp://www.cvc.uab.es/?page_id=7475
Computer Vision Centerhttp://www.cvc.uab.cat CONFIDENTIALITY WARNINGhttp://www.cvc.uab.es/?page_id=7475
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Hans Ekkehard Plesser -
Xavier Otazu -
Xavier Otazu Porter