Ensembles of neurons represent information. In Nengo, we represent that information with real-valued vectors – lists of numbers. In this example, we will represent a two-dimensional vector with a single ensemble of leaky integrate-and-fire neurons.
Step 1: Create the network¶
Our model consists of a single ensemble, which we will call
Neurons. It will represent a two-dimensional signal.
%matplotlib inline import matplotlib.pyplot as plt import numpy as np import nengo model = nengo.Network(label="2D Representation") with model: # Our ensemble consists of 100 leaky integrate-and-fire neurons, # and represents a 2-dimensional signal neurons = nengo.Ensemble(100, dimensions=2)
Step 2: Provide input to the model¶
The signal that an ensemble represents varies over time. We will use a simple sine and cosine wave as examples of continuously changing signals.
with model: # Create input nodes representing the sine and cosine sin = nengo.Node(output=np.sin) cos = nengo.Node(output=np.cos)
Step 3: Connect the input to the ensemble¶
with model: # The indices in neurons define which dimension the input will project to nengo.Connection(sin, neurons) nengo.Connection(cos, neurons)
Step 4: Probe outputs¶
Anything that is probed will collect the data it produces over time, allowing us to analyze and visualize it later. Let’s collect all the data produced.
with model: sin_probe = nengo.Probe(sin, "output") cos_probe = nengo.Probe(cos, "output") neurons_probe = nengo.Probe(neurons, "decoded_output", synapse=0.01)
Step 5: Run the model¶
In order to run the model, we have to create a simulator. Then, we can run that simulator over and over again without affecting the original model.
with nengo.Simulator(model) as sim: sim.run(5)
# Plot the decoded output of the ensemble plt.figure() plt.plot(sim.trange(), sim.data[neurons_probe], label="Decoded output") plt.plot(sim.trange(), sim.data[sin_probe], "r", label="Sine") plt.plot(sim.trange(), sim.data[cos_probe], "k", label="Cosine") plt.legend() plt.xlabel("time [s]")
Text(0.5, 0, 'time [s]')