​Dear all,

With NEST 2.16 and onward, connection infrastructure requires connections to be sorted. Sorting is triggered when calling for example Simulate() or GetConnections(). Therefore, if you have stored your connections with GetConnections(), then create more connections, and the connections are sorted again (e.g. calling GetConnections(), then Connect(), then GetConnections() again), the connections you have stored are no longer valid.

Now, with NEST 2.20, a warning is issued when creating more connections after the current connections have been sorted. This has nothing to do with https://github.com/nest/nest-simulator/pull/1251. As Alex Serenko pointed out, GetConnections() should be placed after all your Connect() calls to avoid invalidating stored connections.

There are however a couple problematic cases. The warning is issued when creating more connections on top of already sorted connections. This means that calling other functions that trigger sorting (for example Simulate()) between Connect() calls also triggers the warning, even if you haven't called GetConnections().

A potentially more serious issue is if you are using PyNN. Creating connections in PyNN may automatically store connections in the Projection object, meaning it calls both Connect() and GetConnections(). Creating Projection objects will therefore trigger the warning every time. Furthermore, creating more than one PyNN Projection object may invalidate the connections stored in all but the last Projection created.

Best,

Håkon

________________________________ Fra: Carlos Gutierrez carlosengutierrez@gmail.com Sendt: 28. februar 2020 11:30 Til: NEST User Mailing List Emne: [NEST Users] Re: warning: 'GetConnections' are now invalid

Dear All, In tested a model that uses several calls to GetConnections for wiring multiple receptors. I tested it in 2.18 and 2.20, with different master seeds. The results are consistent. However, I would like to understand the meaning of that “warning”. Thanks, Carlos.

On Wed, Feb 26, 2020 at 18:49 Carlos Gutierrez <carlosengutierrez@gmail.commailto:carlosengutierrez@gmail.com> wrote: Dear All, I am experiencing the same issue changing from NEST 2.18 to 2.20. Apparently is an error masked as a "warning". I was reading the release notes -->> https://github.com/nest/nest-simulator/releases/tag/v2.20.0 and there is a fix for GetConnections -->> https://github.com/nest/nest-simulator/pull/1251 Probably an error was introduced in that change. Please can you help. Regards, Carlos.

On Thu, Feb 20, 2020 at 9:57 PM Lea Steffen <steffen@fzi.demailto:steffen@fzi.de> wrote:

Hi everybody,

I switched from Nest 2.16 to 2.20 and now I get this warning message:

ConnectionManager [Warning]: New connections created, connection descriptors previously obtained using 'GetConnections' are now invalid

This happens at several parts in my code while building synapses with 'sim.Projection(...)'. I use a 'FromListConnector' and 'STDPMechanism' as synapse_type.

I neversaw this warning in the previous Nest version, is it something to be concerned about?

I am not quite sure what it is trying to tell me.

Thanks in advance, Lea

......................................................... M. Sc. Lea Steffen Wissenschaftlicher Mitarbeiter | Research Scientist Intelligent Systems and Production Engineering (ISPE) Interactive Diagnosis and Service Systems (IDS)

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