Feedforward

[tonydavis629]

Pull Request Template

Description

Adds in a fundamental deepchem layer multilayer perceptron (MLP). This is a simple fully connected feed forward network.

I named it MLP instead of feedforward, since even though feedforward is a common term for it, it can also mean a general network with no cycles. I did not include dropout for the input layer, as this seems to be the common implementation of dropout. Specifying 0 layers will return the input, 1 layer is a single linear layer, and 2+ layers adds additional linear+dropout layers.

I do have a mypy error on activation_fn:
deepchem/models/layers.py:100: error: Incompatible default for argument "activation_fn" (default has type "None", argument has type "Callable[..., Any]")

I'm not really sure what is the problem there, if someone has any input.

Type of change

Please check the option that is related to your PR.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
  • In this case, we recommend to discuss your modification on GitHub issues before creating the PR
• Documentations (modification for documents)

Checklist

• My code follows the style guidelines of this project
  • Run yapf -i <modified file> and check no errors (yapf version must be 0.32.0)
  • Run mypy -p deepchem and check no errors
  • Run flake8 <modified file> --count and check no errors
  • Run python -m doctest <modified file> and check no errors
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New unit tests pass locally with my changes
• I have checked my code and corrected any misspellings

[rbharath]

Reviewed offline with @tonydavis629

• Yapf changes need to be made in a separate PR
• Rename to MultilayerPerceptron

[rbharath]

Tentative approval, couple of minor formatting fixes remain. Feel free to merge after fixed (discussed offline)

[tonydavis629]

I actually don't have merge permissions so if @rbharath or @gusty1g you could give me permissions I can merge this in.