Signal Propagation

The Framework for Unifying Learning and Inference in a Forward Pass

A python package for training parameterized models (e.g. neural networks) via the same forward pass used for inference. This package is for PyTorch.

Signal Propagation (sigprop) is the forward pass learning library for developing and deploying continuous, asynchronous, and parallel (lifelong) learning algorithms on CPUs, GPUs, neuromorphics, and edge devices. continuous, asynchronous, and parallel

Run the Examples and view the Quick Start for implementions details, experiments,, and more.

Documentation for the package is below.

A guide and tutorial on forward learning is available at:
https://amassivek.github.io/sigprop

The paper detailing the framework for forward learning is available at:
https://arxiv.org/abs/2204.01723

TOC

1. Install
2. Quick Start
3. Examples
4. Documentation
5. Development

1. Install

1.1. Production

Install

pip install https://github.com/amassivek/signalpropagation/archive/main.tar.gz

1.2. Development

1. Clone the repo

git clone https://github.com/amassivek/signalpropagation.git

2. cd

cd signalpropagation

3. install in development mode

pip install -e .

4. now you may development on signal propagation

5. then, submit a pull request

2. Quick Start

2.1. Examples
2.2. Implement a Model

2.1. Use Examples

git clone https://github.com/amassivek/signalpropagation.git
cd signalpropagation
pip install -e .
cd examples
chmod +x examples.sh
./examples.sh

2.2 Implement a Model

This quick start uses the forward learning model from Example 2, but on a simple network:
Example 2: Input Target Max Rand

Concept overview of Signal Propagation:

• There is a signal, placed at the front of the network.
• Their are propagators, wrapped around each layer.

1. Install the sigprop package

git clone https://github.com/amassivek/signalpropagation.git
cd signalpropagation
pip install -e .
cd <your_code_directory>

2. Go to the file for network model.

Open the python file with the model you are configuring to use signal propagation.

3. Add the import statement.

import sigprop

4. Select the forward learning model.

Pick a signal, a propagator, and a model for using forward learning. Below are good defaults.

This forward learning model trains each layer of the network as soon as the layer receives an input and target, so training and inference are united and act together. This forward learning model is the base model, and will conveniantly take take of the inputs and outputs during learning and inference.

sigprop.models.Forward

This signal model learns a projection of the input and the target (i.e. context) to the same dimension.

sigprop.signals.ProjectionContextInput

This propagator model takes in any loss function (i.e. callable) to train a network layer. Currently, propagators for signals have different router logic than hidden layers. So, we use a different propagator class for the signal.

sigprop.propagators.signals.Loss
sigprop.propagators.Loss

We pair it with the following loss function.

sigprop.loss.v9_input_target_max_all

A side note. Alternatively, sigprop.propagators.signals.Fixed may be used when the signal is constructed instead of learned, such as a fixed projection or overlay. Here if we replace Loss with Fixed, then the above signal model will be treated as fixed projection. In this case, we would no longer use a loss function.

5. Setup a manager (optional).

Setup a manager to configure defaults to help add signal propagation to an existing model. Managers are helper classes.

Managers are particularly helpful when adding propagators to layers of an existing model. Each network layer is wrapped in a propagator, so it may learn on its own. As we will see below, managers make wrapping layers quick.

sp_manager = sigprop.managers.Preset(
    sigprop.models.Forward,
    sigprop.propagators.Loss,
    sigprop.propagators.signals.Loss,
    build_optimizer
)

We wrote a method to build an optimizer for each layer of the network, since each layer learns independently from the other layers. The manager will call this method with a layer to get an optimizer and then give the optimizer to a propagator to train the layer.

def build_optimizer(module, lr=0.0004, weight_decay=0.0):
    p = list(module.parameters())
    if len(p) == 0:
        return None
    optimizer = optim.Adam(
        p, lr=lr,
        weight_decay=weight_decay)
    return optimizer

6. Configure propagator ahead of time. (optional)

If we are using a manager, we do this step. Otherwise, we skip this step.

Each network layer is wrapped in a propagator, so the layer may learn on its own. Here, we configure defaults for propagators ahead of time, so we may easily wrap layers without having to specify an individual configuration for each layer. Here we set the default loss.

sp_manager.config_propagator(
    loss=sigprop.loss.v9_input_target_max_all
)

7. Setup the signal.

• num_classes is the number of classes.
• hidden_dim is the size of the first hidden dim. Here it is the same as the input dim.

hidden_dim = input_dim
hidden_ch = 128
input_shape = (num_classes,)
output_shape = (hidden_ch, hidden_dim, hidden_dim)
signal_target_module = nn.Sequential(
    nn.Linear(
        int(shape_numel(input_shape)),
        int(shape_numel(output_shape)),
        bias=False
    ),
    nn.LayerNorm(shape_numel(output_shape)),
    nn.ReLU()
)
signal_input_module = nn.Sequential(
    nn.Conv2d(
        3, output_shape[0], 3, 1, 1,
        bias=False
    ),
    nn.BatchNorm2d(output_shape[0]),
    nn.ReLU()
)

sp_signal = sigprop.signals.ProjectionContextInput(
    signal_target_module, signal_input_module,
    input_shape, output_shape
)
# convert labels to a one-hot vector
sp_signal = nn.Sequential(
    sigprop.signals.LabelNumberToOnehot(
        num_classes
    ),
    sp_signal
)

There are two options for wrapping the signal with a propagator:

Option 1, if we are using a manager

sp_signal = sp_manager.set_signal(
    sp_signal,
    loss=sigprop.loss.v9_input_target_max_all
)

Option 2, if we choose to not use a manager.

sp_signal = sigprop.propagators.signals.Loss(
    sp_signal,
    optimizer=build_optimizer(sp_signal),
    loss=sigprop.loss.v9_input_target_max_all
)

Note, we by default feed in a vector as the context. For labels, this means converting to a one_hot vector of type float. We use a formatter, such as LabelNumberToOnehot and place it before the signal (refer to Add a new Signal).

8. Wrap network layers with propagators.

The last layer is trained normally, so we use the identity operation.

Below are the network layers.

layer_1 = nn.Sequential(
    nn.Conv2d(
        hidden_ch, hidden_ch*2, 3, 2, 1,
        bias=False
    ),
    nn.BatchNorm2d(output_shape[0]),
    nn.ReLU()
)
layer_2 = nn.Sequential(
    nn.Conv2d(
        hidden_ch*2, hidden_ch*4, 3, 2, 1,
        bias=False
    ),
    nn.BatchNorm2d(output_shape[0]),
    nn.ReLU()
)
layer_output = nn.Sequential(
    nn.Linear(
        int(input_dim//2**2),
        int(num_classes),
        bias=True
    )
)

There are two options to wrap the layers with propagators.

Option 1, if we are using a manager.

layer_1 = sp_manager.add_propagator(layer_1)
layer_2 = sp_manager.add_propagator(layer_2)
layer_output = sp_manager.add_propagator(layer_output, sigprop.propagators.Identity)

Option 2, if we choose to not use a manager.

from sigprop import propagators
layer_1 = propagators.Loss(
    layer_1,
    optimizer=build_optimizer(layer_1),
    loss=sigprop.loss.v9_input_target_max_all
)
layer_2 = propagators.Loss(
    layer_2,
    optimizer=build_optimizer(layer_2),
    loss=sigprop.loss.v9_input_target_max_all
)
layer_output = propagators.Identity(
    layer_output,
    optimizer=build_optimizer(layer_output),
    loss=sigprop.loss.v9_input_target_max_all
)

9. Create the network.

Below is the network model:

network = nn.Sequential(
    layer_1,
    layer_2,
    layer_output,
)

There are two options to wrap the network model in a sigprop model.

Option 1, if we are using a manager.

network = sp_manager.set_model(network)

Option 2, if we choose to not use a manager.

network = sigprop.models.Forward(network, sp_signal)

10. train the network.

model.train()

for batch, (data, target) in enumerate(train_loader):

    output = model(data, target)

    loss = F.cross_entropy(output, target)
    optimizer.zero_grad()
    loss.backward()
    optimizer.step()

11. inference from network.

model.eval()

acc_sum = 0.
count = 0.

for batch, (data, target) in enumerate(test_loader):

    output = model(data, None)

    pred = output.argmax(1)
    acc_mask = pred.eq(target)
    acc_sum += acc_mask.sum()
    count += acc_mask.size(0)

acc = acc_sum / count

3. Examples

Here are a few examples. More will be added.

Example 2: Input Target Max Rand

ex2_input_target_max_rand.py

This example feeds the inputs x (e.g. images) and their respective targets t (e.g. labels) as pairs (or one after the other). Given pair x_i,t_i, this example selects the closest matching pair x_j,t_j to compare with. If there are multiple equivalent matching pairs, it randomly selects one.

Example 4: Input Target Top-K

ex4_input_target_topk.py

This example feeds the inputs x (e.g. images) and their respective targets t (e.g. labels) as pairs (or one after the other). Given pair x_i,t_i, this example selects the top k closest matching pair x_j,t_j to compare with.

This example demonstrates how to add a monitor to each loss and display metrics for each layer wrapped with a propagator.

4. Documentation

Refer to sections 2 and 3 for examples with explainations.

4.1. Signals

sigprop/signals

Signals generate the signal for learning, then forward it to the first layer. This is taken as the first layer of the network. Or, if a fixed project of the target is used, i.e. there is no learning, then this takes place before the first layer of the network.

4.2. Propagators

sigprop/propagators

Propagators train each network layer and forward the signal from one layer to the other. Each network layer is wrapped in a propagator, so the layer may learn on its own.

4.3. Models

sigprop/models

Models handle the input and output when forward learning. By default, they are not necessary, only signals and propagators are necessary (i.e. signal propagation). However, models provide conveniance functionality for common routines when using signals and propagators.

4.4. Managers

sigprop/managers

Managers allow for upfront configuration (defaults) of signals, propagators, and models. Upfront configuration is helpful in scenerios where signal propagation is wrapping an existing model. For example, we may use the manager to wrap layers in an already existing model. Refer the the examples for a demonstration.

4.5. Functional

sigprop/functional

The functional interface to signal propagation.

4.6. Monitors

sigprop/monitors

Monitor signals, propagators, and modules to record and display metrics. In Example 4: Input Target Top-K, a monitor is wraps the loss to display metrics on the loss and accuracy for each layer wrapped with a propagator; in other words, it displays layer level metrics.

5. Development

5.1. Add a New Loss

Losses are functions or a callable.

Refer to folder sigprop/loss for examples of losses.

Example new implementation:

def new_loss(sp_learn,h1,t1,h0,t0,y_onehot):
    l = #calc loss

    return l

Example new implementation:

class NewLoss(sigprop.loss.Loss):
    def __init__(self):
        super().__init__()

    def forward(sp_learn,h1,t1,h0,t0,y_onehot):
        l = #calc loss

        return l

5.2. Add a New Signal

There is the signal generator and the optional signal formatter.

Generator

Refer to file sigprop/signals/generators.py for examples of signals.

Note, the signal generators return the original input (h0) and context (t0). This provides flexibility for fixing up the input and context before it is used for learning (e.g. reshape). For example, apply a formatter.

Example new implementation:

from sigprop import signals

class MySignalGenerator(signals.Generator):
    def __init__(self, module, input_shape, output_shape):
        super().__init__()
        self.input_shape = input_shape
        self.output_shape = output_shape
        self.module = module

    def forward(self, input):
        h0, t0 = input
        t1 = self.module(t0.flatten(1)).view(t0.shape[0:1]+self.output_shape)
        h1 = h0
        return h1, t1, h0, t0

Formatter

The formatter is optional.

Refer to file sigprop/signals/formatter.py for examples of formatters.

Example new implementation:

from sigprop import signals

class MySignalFormatter(signals.Formatter):
    def forward(self, input):
        h0, t0 = input
        if t0 is not None:
            t0 = F.one_hot(torch.arange(t0.shape[1], device=t0.device),t0.shape[1]).float()
        return h0, t0

5.3. Add a New Propagator

There are two types of propagators: one that learn and ones that do not.

Learn

Refer to file sigprop/propagators/learn.py for examples of propagators that learn.

Currently, propagators for signals have different router logic than hidden layers. So, we use a different propagator class for the signal.

Example new implementation:

from sigprop import propagators

class MyLearnPropagator(propagators.Learn):
    def loss_(self,h1,t1,h0,t0,y_onehot):
        loss = # calculate a loss
        return loss

    def train_(self,h1,t1,h0,t0,y_onehot):
        loss = self.loss_(h1,t1,h0,t0,y_onehot)
        if self.optimizer is not None:
            self.optimizer.zero_grad()
            loss.backward()
            self.optimizer.step()
        return loss.item(), None, None

    def eval_(self,h1,t1,h0,t0,y_onehot):
        loss = self.loss_(h1,t1,h0,t0,y_onehot)
        return loss.item(), None, None

class MyLearnPropagatorForSignals(propagators.signals.Learn):
    def loss_(self,h1,t1,h0,t0,y_onehot):
        loss = # calculate a loss
        return loss

    def train_(self,h1,t1,h0,t0,y_onehot):
        loss = self.loss_(h1,t1,h0,t0,y_onehot)
        if self.optimizer is not None:
            self.optimizer.zero_grad()
            loss.backward()
            self.optimizer.step()
        return loss.item(), None, None

    def eval_(self,h1,t1,h0,t0,y_onehot):
        loss = self.loss_(h1,t1,h0,t0,y_onehot)
        return loss.item(), None, None

Other

Refer to file sigprop/propagators/other.py for examples of propagators that do not learn.

Example new implementation:

from sigprop import propagators

class MyPropagator(propagators.Propagator):
    def __init__(self, module):
        super().__init__()

        self.module = module

    def forward(self, input):
        h0, t0, y_onehot = input

        h1 = self.module(h0)
        t1 = t0

        return (h1, t1, y_onehot)

5.4. Add a New Model

Refer to file sigprop/models/model.py for examples of forward learning models.

Example new implementation:

from sigprop import models

class MyModel(models.Model):
    def __init__(self, model, signal):
        super().__init__(model, signal)

    def forward(self, input):
        x, y_onehot = input
        h0, t0 = self.signal((x, y_onehot, y_onehot))
        h1, t1, y_onehot = self.model((h0, t0, y_onehot))
        return h1