Errors adding synapses with custom connectivity update models

[jhnnsnk]

I am trying to add multiple synapses in one custom connectivity update, but it fails:

TestConnUpdateModel = create_custom_connectivity_update_model(
    class_name="TestConnUpdateModel",
    row_update_code="""
    if (true) {
        // this works for idPost = 0 or 1
        unsigned int idPost = 0;
        add_synapse(idPost);
    }
    else{
        // this doesn't work
        for (unsigned int idPost = 0; idPost < 2; idPost++){
            add_synapse(idPost);
        }
    }
    """
)

When I connect a neuron population with 4 neurons to itself, set the condition above to false, and trigger the update, the output is:

customUpdate.cc:51: void customUpdateUpdateConnectivity(float): block: [0,0,0], thread: [0,0,0] Assertion `group->rowLength[lid] < group->rowStride` failed.
customUpdate.cc:51: void customUpdateUpdateConnectivity(float): block: [0,0,0], thread: [1,0,0] Assertion `group->rowLength[lid] < group->rowStride` failed.
customUpdate.cc:51: void customUpdateUpdateConnectivity(float): block: [0,0,0], thread: [2,0,0] Assertion `group->rowLength[lid] < group->rowStride` failed.
customUpdate.cc:51: void customUpdateUpdateConnectivity(float): block: [0,0,0], thread: [3,0,0] Assertion `group->rowLength[lid] < group->rowStride` failed.
2024-05-12 21:41:19.978 ERROR [1560675] [{anonymous}::Array::free@163] backend.cc: 163: cuda runtime error 710: device-side assert triggered

Could you please let me know what I am doing wrong?

[neworderofjamie]

How did you initially setup the connectivity? I suspect you need to increase the SynapseGroup.max_connections (https://genn-team.github.io/genn/documentation/5/source/pygenn.html#pygenn.SynapseGroup.max_connections) to let GeNN know what your maximum fan-out will be

[jhnnsnk]

Cool, that fixed it, thank you! Indeed I had started from a rather unconnected network.