Source code for geomstats.geometry.general_linear

"""Module exposing the GeneralLinear group class."""

import geomstats.algebra_utils as utils
import geomstats.backend as gs
from geomstats.geometry.base import OpenSet
from geomstats.geometry.lie_algebra import MatrixLieAlgebra
from geomstats.geometry.lie_group import MatrixLieGroup
from geomstats.geometry.matrices import Matrices

[docs]class GeneralLinear(MatrixLieGroup, OpenSet): """Class for the general linear group GL(n) and its identity component. If `positive_det=True`, this is the connected component of the identity, i.e. the space of matrices with positive determinant. Parameters ---------- n : int Integer representing the shape of the matrices: n x n. positive_det : bool Whether to restrict to the identity connected component of the general linear group, i.e. matrices with positive determinant. Optional, default: False. """ def __init__(self, n, positive_det=False, **kwargs): ambient_space = Matrices(n, n) kwargs.setdefault("dim", n**2) kwargs.setdefault("metric", ambient_space.metric) super(GeneralLinear, self).__init__( ambient_space=ambient_space, n=n, lie_algebra=SquareMatrices(n), **kwargs ) self.positive_det = positive_det
[docs] def projection(self, point): r"""Project a matrix to the general linear group. As GL(n) is dense in the space of matrices, this is not a projection per se, but a regularization if the matrix is not already invertible: :math:`X + \epsilon I_n` is returned where :math:`\epsilon=gs.atol` is returned for an input X. Parameters ---------- point : array-like, shape=[..., dim_embedding] Point in embedding manifold. Returns ------- projected : array-like, shape=[..., dim_embedding] Projected point. """ belongs = self.belongs(point) regularization = gs.einsum( "...,ij->...ij", gs.where(~belongs, gs.atol, 0.0), self.identity ) projected = point + regularization if self.positive_det: det = gs.linalg.det(point) return utils.flip_determinant(projected, det) return projected
[docs] def belongs(self, point, atol=gs.atol): """Check if a matrix is invertible and of the right shape. Parameters ---------- point : array-like, shape=[..., n, n] Matrix to be checked. atol : float Tolerance threshold for the determinant. Returns ------- belongs : array-like, shape=[...,] Boolean denoting if point is in GL(n). """ has_right_size = self.ambient_space.belongs(point) if gs.all(has_right_size): det = gs.linalg.det(point) return det > atol if self.positive_det else gs.abs(det) > atol return has_right_size
[docs] def random_point(self, n_samples=1, bound=1.0, n_iter=100): """Sample in GL(n) from the uniform distribution. Parameters ---------- n_samples : int Number of samples. Optional, default: 1. bound: float Bound of the interval in which to sample each matrix entry. Optional, default: 1. n_iter : int Maximum number of trials to sample a matrix with positive det. Optional, default: 100. Returns ------- samples : array-like, shape=[..., n, n] Point sampled on GL(n). """ n = self.n sample = [] n_accepted, iteration = 0, 0 criterion_func = (lambda x: x) if self.positive_det else gs.abs while n_accepted < n_samples and iteration < n_iter: raw_samples = gs.random.normal(size=(n_samples - n_accepted, n, n)) dets = gs.linalg.det(raw_samples) criterion = criterion_func(dets) > gs.atol if gs.any(criterion): sample.append(raw_samples[criterion]) n_accepted += gs.sum(criterion) iteration += 1 if n_samples == 1: return sample[0][0] return gs.concatenate(sample)
[docs] @classmethod def orbit(cls, point, base_point=None): r""" Compute the one-parameter orbit of base_point passing through point. Parameters ---------- point : array-like, shape=[n, n] Target point. base_point : array-like, shape=[n, n], optional Base point. Optional, defaults to identity if None. Returns ------- path : callable One-parameter orbit. Satisfies `path(0) = base_point` and `path(1) = point`. Notes ----- Denoting `point` by :math:`g` and `base_point` by :math:`h`, the orbit :math:`\gamma` satisfies: .. math:: \gamma(t) = {\mathrm e}^{t X} \cdot h \\ \quad \text{with} \quad\\ {\mathrm e}^{X} = g h^{-1} The path is not uniquely defined and depends on the choice of :math:`V` returned by :py:meth:`log`. Vectorization ------------- Return a collection of trajectories (4-D array) from a collection of input matrices (3-D array). """ tangent_vec = cls.log(point, base_point) def path(time): vecs = gs.einsum("t,...ij->...tij", time, tangent_vec) return cls.exp(vecs, base_point) return path
[docs]class SquareMatrices(MatrixLieAlgebra): """Lie algebra of the general linear group. This is the space of matrices. Parameters ---------- n : int Integer representing the shape of the matrices: n x n. """ def __init__(self, n): super(SquareMatrices, self).__init__(n=n, dim=n**2) self.mat_space = Matrices(n, n) def _create_basis(self): """Create the canonical basis of the space of matrices.""" return self.mat_space.basis
[docs] def basis_representation(self, matrix_representation): """Compute the coefficient in the usual matrix basis. This simply flattens the input. Parameters ---------- matrix_representation : array-like, shape=[..., n, n] Matrix. Returns ------- basis_representation : array-like, shape=[..., dim] Representation in the basis. """ return self.mat_space.flatten(matrix_representation)
[docs] def matrix_representation(self, basis_representation): """Compute the matrix representation for the given basis coefficients. This simply reshapes the input into a square matrix. Parameters ---------- basis_representation : array-like, shape=[..., dim] Coefficients in the basis. Returns ------- matrix_representation : array-like, shape=[..., n, n] Matrix. """ return self.mat_space.reshape(basis_representation)