brian2-loihi 0.4.0

A Loihi emulator based on Brian2

A Loihi emulator based on Brian2

The package extends Brian2 classes such that they match Loihi simulations. While the neuron and synapse model results in an exact match to Loihi, the pre- and post-synaptic traces have very small variations from the Loihi chip due to stochastic rounding.

Further details are explained in a paper coming soon.

Installation

pip install brian2-loihi

Usage

Five Brian2 classes are extended. Available parameters are reported below. Further down you find example code.

Note:

• It is important to use a LoihiNetwork. The Brian2 magic network approach is not supported.
• Don't change the defaultclock.dt value. It is set to match Loihi.
• Don't reorder the network simulation schedule.

First import the package as:

from brian2_loihi import *

The following classes can be used:

LoihiNetwork

Extends the Network class from Brian2 and supports the same parameters.

LoihiNeuronGroup

Extends the NeuronGroup class from Brian2 and supports the following parameters:

• N (int): Number of neurons in the group.
• refractory (int, 1...64, optional): The refactory period of the neuron.
• threshold_v_mant (int, 0...131071, optional): The mantissa of the membrane voltage threshold.
• decay_v (int, 0...4096, optional): The membrane voltage decay (note that tau_v = 4096/decay_v)
• decay_I (int, 0...4096, optional): The current decay (note that tau_I = 4096/decay_I)

LoihiSynapses

Extends the Synapses class from Brian2 and supports the following parameters:

• source (SpikeSource): The source of spikes, e.g. a NeuronGroup.
• target (Group, optional): The target of the spikes, typically a NeuronGroup. If none is given, the same as source().
• delay (int, optional): The synaptic delay.
• dw (str, optional): Learning rule, using the pre- and post-synaptic traces. Also constant values are allowed. Note that only *, - and + is allowed.
• w_exp (int, optional): Weight exponent which scales the weights by 2^(6 + w_exp). The weight exponent can be between -8 and 7.
• sign_mode (int, optional): Defines if the synapses are mixed (1), excitatory (2) or inhibitory (3). Excitatory synapses are default. synapse_sign_mode can be used for defining the sign mode.
• num_weight_bits (int, optional): Defines the precision of the weight, default is 8 bits. num_weight_bits is in a range between 0 and 8.
• imp_x1 (int, optional): The impulse of the first synaptic pre trace x1.
• tau_x1 (int, optional): The time constant of the first synaptic pre trace x1.
• imp_x2 (int, optional): The impulse of the first synaptic pre trace x2.
• tau_x2 (int, optional): The time constant of the first synaptic pre trace x2.
• imp_y1 (int, optional): The impulse of the first synaptic post trace y1.
• tau_y1 (int, optional): The time constant of the first synaptic pre trace y1.
• imp_y2 (int, optional): The impulse of the first synaptic post trace y2.
• tau_y2 (int, optional): The time constant of the first synaptic pre trace y2.
• imp_y3 (int, optional): The impulse of the first synaptic post trace y3.
• tau_y3 (int, optional): The time constant of the first synaptic pre trace y3.

LoihiStateMonitor

Extends the StateMonitor class from Brian2 and supports the following parameters:

• source (Group): Which object to record values from.
• variable (str): Which variables to record, check the state object for details.
• record (bool, sequence of ints): Which indices to record, nothing is recorded for False, everything is recorded for True (warning: may use a great deal of memory), or a specified subset of indices.
• order (int, optional): The priority of of this group for operations occurring at the same time step and in the same scheduling slot. Defaults to 0.

LoihiSpikeMonitor

Extends the SpikeMonitor class from Brian2 and supports the following parameters:

• source (Group): Which object to record values from.
• variable (str): Which variables to record at the time of the spike (in addition to the index of the neuron). Can be the name of a variable or a list of names
• record (bool, sequence of ints): Which indices to record, nothing is recorded for False, everything is recorded for True (warning: may use a great deal of memory), or a specified subset of indices.
• order (int, optional): The priority of of this group for operations occurring at the same time step and in the same scheduling slot. Defaults to 0.

LoihiSpikeGeneratorGroup

Extends the SpikeGeneratorGroup class from Brian2 and supports the following parameters:

• N (int): The number of "neurons" in this group
• indices (array of integers): The indices of the spiking cells
• times (list (int)): The spike times for the cells given in indices. Has to have the same length as indices and has to be integer (without time units)
• period (int, optional): If this is specified, it will repeat spikes with this period. A period of 0 means not repeating spikes.
• order (int, optional): The priority of of this group for operations occurring at the same time step and in the same scheduling slot. Defaults to 0.
• sorted (bool, optional): Whether the given indices and times are already sorted. Set to True if your events are already sorted (first by spike time, then by index), this can save significant time at construction if your arrays contain large numbers of spikes. Defaults to False.

Example

Follows soon