class_docstr: Class for the space of matrices (m, n).
  
  Parameters
  ----------
  m, n : int
      Integers representing the shapes of the matrices: m x n.
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docstr: Check if a square matrix is lower triangular.
  
  Parameters
  ----------
  mat : array-like, shape=[..., n, n]
      Matrix.
  atol : float
      Absolute tolerance.
      Optional, default : backend atol.
  
  Returns
  -------
  is_tril : array-like, shape=[...,]
      Boolean evaluating if the matrix is lower triangular
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code: def is_lower_triangular(cls, mat, atol=gs.atol):
      """Check if a square matrix is lower triangular.
  
      Parameters
      ----------
      mat : array-like, shape=[..., n, n]
          Matrix.
      atol : float
          Absolute tolerance.
          Optional, default : backend atol.
  
      Returns
      -------
      is_tril : array-like, shape=[...,]
          Boolean evaluating if the matrix is lower triangular
      """
      return cls.equal(mat, gs.tril(mat), atol)
  
imports: import logging
  import math
  from functools import reduce
  import geomstats.backend
  import geomstats.errors
  from geomstats.algebra_utils import flip_determinant, from_vector_to_diagonal_matrix
  from geomstats.geometry.base import MatrixVectorSpace
  from geomstats.geometry.euclidean import EuclideanMetric
  from geomstats.vectorization import repeat_out
label_desc: Use image node_id 12 for calling the Matrices obj's underlying member method code with example usage: obj.is_lower_triangular(cls, mat, atol) and returns: cls