Refractoriness for custom events

[thesamovar]

We should probably allow for this possibility. Syntax should be straightforward, allow for a dict instead of string/quantity.

[mstimberg]

Agreed, makes sense.

[maverick4code]

@thesamovar @mstimberg I think we can tweak refractory parameter in NeuronGroup to accept a dictionary. This would allow us to specify refractory period for custom events and default spike events.

Here is a simple example(reference):

from brian2 import *
"""Creates a NeuronGroup with a spike event (v > 1, 5ms) and a custom event (x > 1, x < 0.5)."""
eqs = '''
dv/dt = -v / (10*ms) : 1
dx/dt = -x / (20*ms) : 1
'''
G = NeuronGroup(1, eqs, threshold='v > 1', reset='v = 0', events={'custom_event': 'x > 1'}, 
                refractory={'spike': 5*ms, 'custom_event': 'x < 0.5'})

The old code with just 5*ms would still work for spike.

If any additional thoughts, please let me know.

[mstimberg]

Yes, this is what we had in mind syntaxwise. For implementing it, we'd have to generalize the Thresholder class and the associated templates a bit. We'd have to add new variables for each custom event that correspond to not_refractory and lastspike, and use these names in the code/template. Very similar to the changes we did when we introduced custom events originally, where we replaced the single spikespace variable by multiple eventspace variables.

[maverick4code]

@thesamovar @mstimberg, I have reviewed the current implementation in brian2/groups/neurongroup.py and tried to get a solution.

1. NeuronGroup
   I have updated the __init__ method in brian2/groups/neurongroup.py to support the refractory parameter.

class NeuronGroup(Group):
    def __init__(self, N, model, threshold=None, reset=None, refractory=None, events=None,):
        
        if events is None:
            events = {}
        self.events = {'spike': threshold} if threshold else {}
        self.events.update(events)

        if refractory is not None:
            if isinstance(refractory, (str, Quantity)):
                refractory = {'spike': refractory}
            elif isinstance(refractory, dict):
              
                for event in refractory:
                    if event not in self.events:
                        raise ValueError(f"Unknown event '{event}' in refractory dictionary.")
            else:
                raise TypeError("refractory must be a string, Quantity, or dictionary")
        else:
            refractory = {}
        self._refractory = refractory

        # calling parent class, setting up variables
       . . .

2. Variables setup
   In the _create_variables method, we can define variables for each event with a refractory period.

def _create_variables(self):
    if 'spike' in self.events:
        self.variables.add_array('_lastspike', size=self.N, dtype=float, constant=False, value=-1e100)

    for event, refr in self._refractory.items():
        event_name = event.replace(' ', '_')  
        self.variables.add_array(f'_lastevent_{event_name}', size=self.N, dtype=float, 
                                constant=False, value=-1e100)
        
        if isinstance(refr, Quantity):
            self.variables.add_array(f'_refractory_until_{event_name}', size=self.N, dtype=float, 
                                    constant=False, value=-1e100)
            # not_refractory as a time-based condition
            self.variables.add_subexpression(f'not_refractory_{event_name}', 
                                             f't >= _refractory_until_{event_name}')
        elif isinstance(refr, str):
            self.variables.add_subexpression(f'not_refractory_{event_name}', f'not ({refr})')

    # events without refractory
    for event in self.events:
        event_name = event.replace(' ', '_')
        if event not in self._refractory:
            self.variables.add_subexpression(f'not_refractory_{event_name}', 'True')

[mstimberg]

Hi @maverick4code. From a cursory look, this seems correct to me. Could you open a (draft) pull request so that we more easily play with and look at the code? Thanks!