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# TensorNodes¶

TensorNodes allow parts of a model to be defined using TensorFlow and smoothly integrated with the rest of a Nengo model. TensorNodes work very similarly to a regular Node, except instead of executing arbitrary Python code they execute arbitrary TensorFlow code.

The TensorFlow code is defined in a function or callable class (tensor_func). This function accepts the current simulation time as input, or the current simulation time and a Tensor x if node.size_in > 0. x will have shape (sim.minibatch_size, node.size_in), and the function should return a Tensor with shape (sim.minibatch_size, node.size_out). node.size_out will be inferred by calling the function once and checking the output, if it isn’t set when the Node is created.

def tensor_func(t [, x]):
print(t)  # current simulation time
print(x)  # input on current timestep (minibatch_size, node.size_in)

return x + 1


If tensor_func has a pre_build attribute, that function will be called once when the model is constructed. This can be used to compute any constant values or set up variables – things that don’t need to execute every simulation timestep.

def pre_build(shape_in, shape_out):
print(shape_in)  # (minibatch_size, node.size_in)
print(shape_out)  # (minibatch_size, node.size_out)


If tensor_func has a post_build attribute, that function will be called after the simulator is created and whenever it is reset. This can be used to set any random elements in the TensorNode or perform any post-initialization setup required by the node (e.g., loading pretrained weights).

def post_build(sess, rng):
print(sess)  # the TensorFlow simulation session object
print(rng)  # random number generator (np.random.RandomState)


tensor_layer is a utility function for constructing TensorNodes, designed to mimic the layer-based model construction style of many deep learning packages. It combines the creation of a TensorNode or Ensemble and a Connection in a single step.

See the TensorNode API for more details, or the examples below for demonstrations of using TensorNodes in practice.