Delaying a connection with a node

Nodes allow for all sorts of advanced behavior that is typically done by modifying of extending the code of a neural simulator. In Nengo, the Node object allows for custom code to run.

In this example, we will implement an n-timestep delayed connection by using a node.



In [ ]:

    
import numpy as np
import nengo
from nengo.utils.functions import whitenoise

model = nengo.Network(label="Delayed connection")
with model:
    # We'll use white noise as input
    input = nengo.Node(output=whitenoise(1, 5, seed=60))
    A = nengo.Ensemble(nengo.LIF(40), dimensions=1)
    nengo.Connection(input, A)

# We'll make a simple object to implement the delayed connection
class Delay(object):
    def __init__(self, dimensions, timesteps=50):
        self.history = np.zeros((timesteps, dimensions))
    def step(self, t, x):
        self.history = np.roll(self.history, -1)
        self.history[-1] = x
        return self.history[0]

dt = 0.001
delay = Delay(1, timesteps=int(0.2 / 0.001))

with model:
    delaynode = nengo.Node(delay.step, size_in=1)
    nengo.Connection(A, delaynode)
    
    # Send the delayed output through an ensemble
    B = nengo.Ensemble(nengo.LIF(40), dimensions=1)
    nengo.Connection(delaynode, B)
    
    # Probe the input at the delayed output
    A_probe = nengo.Probe(A, "decoded_output", synapse=0.01)
    B_probe = nengo.Probe(B, "decoded_output", synapse=0.01)



In [ ]:

    
# Run for 2 seconds
sim = nengo.Simulator(model)
sim.run(2)

# Plot the results
import matplotlib.pyplot as plt
plt.subplot(2, 1, 1)
plt.plot(sim.trange(), sim.data[A_probe], lw=2)
plt.title("Input")
plt.subplot(2, 1, 2)
plt.plot(sim.trange(), sim.data[B_probe], lw=2)
plt.axvline(0.2, c='k')
plt.title("Delayed output")
plt.tight_layout()