Source code for botorch.models.kernels.categorical

#!/usr/bin/env python3
# Copyright (c) Meta Platforms, Inc. and affiliates.
# This source code is licensed under the MIT license found in the
# LICENSE file in the root directory of this source tree.

import torch
from gpytorch.kernels.kernel import Kernel
from torch import Tensor

[docs]class CategoricalKernel(Kernel): r"""A Kernel for categorical features. Computes `exp(-dist(x1, x2) / lengthscale)`, where `dist(x1, x2)` is zero if `x1 == x2` and one if `x1 != x2`. If the last dimension is not a batch dimension, then the mean is considered. Note: This kernel is NOT differentiable w.r.t. the inputs. """ has_lengthscale = True def forward( self, x1: Tensor, x2: Tensor, diag: bool = False, last_dim_is_batch: bool = False, **kwargs ) -> Tensor: delta = x1.unsqueeze(-2) != x2.unsqueeze(-3) dists = delta / self.lengthscale.unsqueeze(-2) if last_dim_is_batch: dists = dists.transpose(-3, -1) else: dists = dists.mean(-1) res = torch.exp(-dists) if diag: res = torch.diagonal(res, dim1=-1, dim2=-2) return res