Source code for tensorly.tenalg.n_mode_product

from .. import backend as T
from ..base import unfold, fold

from tensorly import unfold, fold, vec_to_tensor

[docs]def mode_dot(tensor, matrix_or_vector, mode): """n-mode product of a tensor and a matrix or vector at the specified mode Mathematically: :math:`\\text{tensor} \\times_{\\text{mode}} \\text{matrix or vector}` Parameters ---------- tensor : ndarray tensor of shape ``(i_1, ..., i_k, ..., i_N)`` matrix_or_vector : ndarray 1D or 2D array of shape ``(J, i_k)`` or ``(i_k, )`` matrix or vectors to which to n-mode multiply the tensor mode : int Returns ------- ndarray `mode`-mode product of `tensor` by `matrix_or_vector` * of shape :math:`(i_1, ..., i_{k-1}, J, i_{k+1}, ..., i_N)` if matrix_or_vector is a matrix * of shape :math:`(i_1, ..., i_{k-1}, i_{k+1}, ..., i_N)` if matrix_or_vector is a vector See also -------- multi_mode_dot : chaining several mode_dot in one call """ # the mode along which to fold might decrease if we take product with a vector fold_mode = mode new_shape = list(tensor.shape) if T.ndim(matrix_or_vector) == 2: # Tensor times matrix # Test for the validity of the operation if matrix_or_vector.shape[1] != tensor.shape[mode]: raise ValueError( 'shapes {0} and {1} not aligned in mode-{2} multiplication: {3} (mode {2}) != {4} (dim 1 of matrix)'.format( tensor.shape, matrix_or_vector.shape, mode, tensor.shape[mode], matrix_or_vector.shape[1] )) new_shape[mode] = matrix_or_vector.shape[0] vec = False elif T.ndim(matrix_or_vector) == 1: # Tensor times vector if matrix_or_vector.shape[0] != tensor.shape[mode]: raise ValueError( 'shapes {0} and {1} not aligned for mode-{2} multiplication: {3} (mode {2}) != {4} (vector size)'.format( tensor.shape, matrix_or_vector.shape, mode, tensor.shape[mode], matrix_or_vector.shape[0] )) if len(new_shape) > 1: new_shape.pop(mode) else: new_shape = [1] vec = True else: raise ValueError('Can only take n_mode_product with a vector or a matrix.' 'Provided array of dimension {} not in [1, 2].'.format(T.ndim(matrix_or_vector))) res = T.dot(matrix_or_vector, unfold(tensor, mode)) if vec: # We contracted with a vector, leading to a vector return vec_to_tensor(res, shape=new_shape) else: # tensor times vec: refold the unfolding return fold(res, fold_mode, new_shape)
[docs]def multi_mode_dot(tensor, matrix_or_vec_list, modes=None, skip=None, transpose=False): """n-mode product of a tensor and several matrices or vectors over several modes Parameters ---------- tensor : ndarray matrix_or_vec_list : list of matrices or vectors of length ``tensor.ndim`` skip : None or int, optional, default is None if not None, index of a matrix to skip Note that in any case, `modes`, if provided, should have a length of ``tensor.ndim`` modes : None or int list, optional, default is None transpose : bool, optional, default is False if True, the matrices or vectors in in the list are transposed (the conjugate is used for complex tensors) Returns ------- ndarray tensor times each matrix or vector in the list at mode `mode` Notes ----- If no modes are specified, just assumes there is one matrix or vector per mode and returns: :math:`\\text{tensor }\\times_0 \\text{ matrix or vec list[0] }\\times_1 \\cdots \\times_n \\text{ matrix or vec list[n] }` See also -------- mode_dot """ if modes is None: modes = range(len(matrix_or_vec_list)) decrement = 0 # If we multiply by a vector, we diminish the dimension of the tensor res = tensor # Order of mode dots doesn't matter for different modes # Sorting by mode shouldn't change order for equal modes factors_modes = sorted(zip(matrix_or_vec_list, modes), key=lambda x: x[1]) for i, (matrix_or_vec, mode) in enumerate(factors_modes): if (skip is not None) and (i == skip): continue if transpose: res = mode_dot(res, T.conj(T.transpose(matrix_or_vec)), mode - decrement) else: res = mode_dot(res, matrix_or_vec, mode - decrement) if T.ndim(matrix_or_vec) == 1: decrement += 1 return res