#!/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.
from __future__ import annotations
from collections.abc import Sequence
from dataclasses import dataclass, InitVar
from itertools import chain
from typing import Any
import torch
from botorch.utils.probability.utils import swap_along_dim_
from linear_operator.utils.errors import NotPSDError
from torch import LongTensor, Tensor
from torch.nn.functional import pad
[docs]
def block_matrix_concat(blocks: Sequence[Sequence[Tensor]]) -> Tensor:
rows = []
shape = torch.broadcast_shapes(*(x.shape[:-2] for x in chain.from_iterable(blocks)))
for tensors in blocks:
parts = [x.expand(*shape, *x.shape[-2:]) for x in tensors]
if len(parts) > 1:
rows.append(torch.cat(parts, dim=-1))
else:
rows.extend(parts)
return torch.concat(rows, dim=-2)
[docs]
def augment_cholesky(
Laa: Tensor,
Kbb: Tensor,
Kba: Tensor | None = None,
Lba: Tensor | None = None,
jitter: float | None = None,
) -> Tensor:
r"""Computes the Cholesky factor of a block matrix `K = [[Kaa, Kab], [Kba, Kbb]]`
based on a precomputed Cholesky factor `Kaa = Laa Laa^T`.
Args:
Laa: Cholesky factor of K's upper left block.
Kbb: Lower-right block of K.
Kba: Lower-left block of K.
Lba: Precomputed solve `Kba Laa^{-T}`.
jitter: Optional nugget to be added to the diagonal of Kbb.
"""
if not (Kba is None) ^ (Lba is None):
raise ValueError("One and only one of `Kba` or `Lba` must be provided.")
if jitter is not None:
Kbb = Kbb.clone()
Kbb.diagonal(dim1=-2, dim2=-1).add_(jitter)
if Lba is None:
Lba = torch.linalg.solve_triangular(
Laa.transpose(-2, -1), Kba, left=False, upper=True
)
Lbb, info = torch.linalg.cholesky_ex(Kbb - Lba @ Lba.transpose(-2, -1))
if info.any():
raise NotPSDError(
"Schur complement of `K` with respect to `Kaa` not PSD for the given "
"Cholesky factor `Laa`"
f"{'.' if jitter is None else f' and nugget jitter={jitter}.'}"
)
n = Lbb.shape[-1]
return block_matrix_concat(blocks=([pad(Laa, (0, n))], [Lba, Lbb]))
[docs]
@dataclass
class PivotedCholesky:
step: int
tril: Tensor
perm: LongTensor
diag: Tensor | None = None
validate_init: InitVar[bool] = True
def __post_init__(self, validate_init: bool = True):
if not validate_init:
return
if self.tril.shape[-2] != self.tril.shape[-1]:
raise ValueError(
f"Expected square matrices but `matrix` has shape `{self.tril.shape}`."
)
if self.perm.shape != self.tril.shape[:-1]:
raise ValueError(
f"`perm` of shape `{self.perm.shape}` incompatible with "
f"`matrix` of shape `{self.tril.shape}`."
)
if self.diag is not None and self.diag.shape != self.tril.shape[:-1]:
raise ValueError(
f"`diag` of shape `{self.diag.shape}` incompatible with "
f"`matrix` of shape `{self.tril.shape}`."
)
def __getitem__(self, key: Any) -> PivotedCholesky:
return PivotedCholesky(
step=self.step,
tril=self.tril[key],
perm=self.perm[key],
diag=None if self.diag is None else self.diag[key],
)
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def update_(self, eps: float = 1e-10) -> None:
r"""Performs a single matrix decomposition step."""
i = self.step
L = self.tril
Lii = self.tril[..., i, i].clone().clip(min=0).sqrt()
# Finalize `i-th` row and column of Cholesky factor
L[..., i, i] = Lii
L[..., i, i + 1 :] = 0
L[..., i + 1 :, i] = L[..., i + 1 :, i].clone() / Lii.unsqueeze(-1)
# Update `tril(L[i + 1:, i + 1:])` to be the lower triangular part
# of the Schur complement of `cov` with respect to `cov[:i, :i]`.
rank1 = L[..., i + 1 :, i : i + 1].clone()
rank1 = (rank1 * rank1.transpose(-1, -2)).tril()
L[..., i + 1 :, i + 1 :] = L[..., i + 1 :, i + 1 :].clone() - rank1
L[Lii <= i * eps, i:, i] = 0 # numerical stability clause
self.step += 1
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def pivot_(self, pivot: LongTensor) -> None:
*batch_shape, _, size = self.tril.shape
if pivot.shape != tuple(batch_shape):
raise ValueError("Argument `pivot` does to match with batch shape`.")
# Perform basic swaps
for key in ("perm", "diag"):
tnsr = getattr(self, key, None)
if tnsr is not None:
swap_along_dim_(tnsr, i=self.step, j=pivot, dim=tnsr.ndim - 1)
# Perform matrix swaps; prealloacte buffers for row/column linear indices
size2 = size**2
min_pivot = pivot.min()
tkwargs = {"device": pivot.device, "dtype": pivot.dtype}
buffer_col = torch.arange(size * (1 + min_pivot), size2, size, **tkwargs)
buffer_row = torch.arange(0, max(self.step, pivot.max()), **tkwargs)
head = buffer_row[: self.step]
indices_v1 = []
indices_v2 = []
for i, piv in enumerate(pivot.view(-1, 1)):
v1 = pad(piv, (1, 0), value=self.step).unsqueeze(-1)
v2 = pad(piv, (0, 1), value=self.step).unsqueeze(-1)
start = i * size2
indices_v1.extend((start + v1 + size * v1).ravel())
indices_v2.extend((start + v2 + size * v2).ravel())
indices_v1.extend((start + size * v1 + head).ravel())
indices_v2.extend((start + size * v2 + head).ravel())
tail = buffer_col[piv - min_pivot :]
indices_v1.extend((start + v1 + tail).ravel())
indices_v2.extend((start + v2 + tail).ravel())
interior = buffer_row[min(piv, self.step + 1) : piv]
indices_v1.extend(start + size * interior + self.step)
indices_v2.extend(start + size * piv + interior)
swap_along_dim_(
self.tril.view(-1),
i=torch.as_tensor(indices_v1, **tkwargs),
j=torch.as_tensor(indices_v2, **tkwargs),
dim=0,
)
[docs]
def expand(self, *sizes: int) -> PivotedCholesky:
fields = {}
for name, ndim in {"perm": 1, "diag": 1, "tril": 2}.items():
src = getattr(self, name)
if src is not None:
fields[name] = src.expand(sizes + src.shape[-ndim:])
return type(self)(step=self.step, **fields)
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def concat(self, other: PivotedCholesky, dim: int = 0) -> PivotedCholesky:
if self.step != other.step:
raise ValueError("Cannot conncatenate decompositions at different steps.")
fields = {}
for name in ("tril", "perm", "diag"):
a = getattr(self, name)
b = getattr(other, name)
if type(a) is not type(b):
raise NotImplementedError(f"Types of field {name} do not match.")
if a is not None:
fields[name] = torch.concat((a, b), dim=dim)
return type(self)(step=self.step, **fields)
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def detach(self) -> PivotedCholesky:
fields = {}
for name in ("tril", "perm", "diag"):
obj = getattr(self, name)
if obj is not None:
fields[name] = obj.detach()
return type(self)(step=self.step, **fields)
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def clone(self) -> PivotedCholesky:
fields = {}
for name in ("tril", "perm", "diag"):
obj = getattr(self, name)
if obj is not None:
fields[name] = obj.clone()
return type(self)(step=self.step, **fields)
