Cuda Memory Error on Connections with 0 synapses

[joey-kilgore]

Context - I'm working on smaller scale network models and comparing their network dynamics and potential for scaling. The current model we use has a wide selection of 9-param IZ groups, but some with significantly fewer neurons than another. I know that running smaller scale networks is faster on CPU, but often the networks may have one or two group with >1000 neurons, and one or two groups with <5 neurons, and it would be nice to not have to keep switching between the two.

Problem - Often times we are scaling to the point they may be only 1 neuron in a group, which may have a connection to another group with 1 neuron. While we test different connection probabilities, in this connection from a 1 neuron group to another 1 neuron group, it would often generate a connection with no synapses (based on the connection probability). This would throw a cuda memory error (since it would try and copy the non existent synaptic info)

Fix in my project - I think there are ways for me to avoid this in my work by just forcing probabilities to be 1 if there is a low enough number of neurons. BUT this is something that technically could always occur. For instance if there are 2 neurons in groups being connecting, a probability of 0.5 should work, but would fail 1/16 of the time.

Fix in CARLsim6 - There needs to be a check at synaptic generation for empty connections, and generate a random connection. With that the following steps should occur

• Check for empty connections at generation
• Randomly choose a synapse to create (note that just retrying over and over is probably not a good idea, since it may be a low probability)
• Output a debug message and a user message that a synaptic connection was forcibly chosen
• Update the documentation to note this issue on the Connections page in the user guide

[larsnm]

We will consider this feature request and add a warning message to indicate that the probability was not satisfied.

[joey-kilgore]

Thanks for the reply,
But based on my understanding a warning message is insufficient to fix this since technically speaking any randomly generated network could end up with no connections and fail (though some are extremely unlikely). There should be a requirement of at least one connection and then note a warning if this had occurred.
This is a needed change for anyone using smaller networks, or networks with lots of small groups.

Consider a network with 50 groups of 6 neurons each with a connection probability of 0.5 to every other group. On average 1/64 connections will generate 0 synapses and break CARLsim. Likely this network, would not successfully run on CARLsim because of this error. Even though the network as a whole would have 300 neurons and on average 4500 synapses.