A simple library to convert Drake symbolic expressions to PyTorch functions, which can then be evaluated and differentiated on PyTorch Tensors.

In the interest of computational efficiency, the Drake symbolic expression is first converted to an intermediate SymPy symbolic expression for rewrite simplification; then the simplified expression is converted to a Python function that efficiently computes the final expression via dynamic programming.

This supports both single and vector (via Python lists) expressions, which can be converted to a function of a variable number of arguments. The generated function supports arbitrary prefix batching.

This repository supports direct installation via pip.

pip will attempt to find pydrake already installed, before falling back to installing pip install drake, which is currently only supported on Linux with CPython versions 3.6-3.9. macOS support is in progress.

Due to the significant dependencies required, it is recommended to install in a virtual environment.

python[3] -m venv drake-pytorch
source drake-pytorch/bin/activate
pip install --upgrade pip setuptools wheel
pip install git+https://github.com/DAIRLab/drake-pytorch.git

import pydrake.symbolic as sym
import torch
import drake_pytorch
import numpy as np

x = sym.MakeVectorVariable(2,'x')
y = sym.MakeVectorVariable(2,'y')

# expr is a length-2 list, depending on the x and y variables
expr = [x[0]*x[1], sym.sin(y[1]) * x[0]]

# Convert to a function with two arguments, (x,y)
[func, string] = drake_pytorch.sym_to_pytorch(expr, x, y)

# Create PyTorch inputs and evaluate the function
x_torch = torch.tensor([1.0, 2.0], requires_grad=True)
y_torch = torch.tensor([3.0, 4.0], requires_grad=True)

result = func(x_torch, y_torch)