##### https://github.com/tensorly/tensorly
Revision f7e7962ff272df751da09e08d16cf9978bc37e01 authored by Jean Kossaifi on 03 December 2016, 23:53 UTC, committed by Jean Kossaifi on 03 December 2016, 23:53 UTC
1 parent 1788d26
Tip revision: f7e7962
tucker.py
``````"""
Core operations on Tucker tensors.
"""

from .base import unfold, tensor_to_vec
from .tenalg import multi_mode_dot
from .tenalg import kronecker

# Author: Jean Kossaifi <jean.kossaifi+tensors@gmail.com>

def tucker_to_tensor(core, factors, skip_factor=None, transpose_factors=False):
"""Converts the Tucker tensor into a full tensor

Parameters
----------
core : ndarray
core tensor
factors : ndarray list
list of matrices of shape ``(s_i, core.shape[i])``
skip_factor : 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 lengh of ``tensor.ndim``
transpose_factors : bool, optional, default is False
if True, the matrices or vectors in in the list are transposed

Returns
-------
2D-array
full tensor of shape ``(factors[0].shape[0], ..., factors[-1].shape[0])``

Notes
-----
This implementation is equivalent to:

>>> def tucker_to_tensor(core, factors):
...     for i, matrix in enumerate(factors):
...         if not i:
...             res = mode_dot(core, matrix, i)
...         else:
...             res = mode_dot(res, matrix, i)
...     return res
"""
return multi_mode_dot(core, factors, skip=skip_factor, transpose=transpose_factors)

def tucker_to_unfolded(core, factors, mode=0, skip_factor=None, transpose_factors=False):
"""Converts the Tucker decomposition into an unfolded tensor (i.e. a matrix)

Parameters
----------
core : ndarray
core tensor
factors : ndarray list
list of matrices
mode : None or int list, optional, default is None
skip_factor : 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 lengh of ``tensor.ndim``
transpose_factors : bool, optional, default is False
if True, the matrices or vectors in in the list are transposed

Returns
-------
2D-array
unfolded tensor
"""
return unfold(tucker_to_tensor(core, factors, skip_factor=skip_factor, transpose_factors=transpose_factors), mode)

def tucker_to_vec(core, factors, skip_factor=None, transpose_factors=False):
"""Converts a Tucker decomposition into a vectorised tensor

Parameters
----------
core : ndarray
core tensor
factors : ndarray list
list of factor matrices
skip_factor : 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 lengh of ``tensor.ndim``
transpose_factors : bool, optional, default is False
if True, the matrices or vectors in in the list are transposed

Returns
-------
1D-array
vectorised tensor

Notes
-----
Mathematically equivalent but much slower,
you can obtain the same result using:

>>> def tucker_to_vec(core, factors):
...     return kronecker(factors).dot(tensor_to_vec(core))
"""
return tensor_to_vec(tucker_to_tensor(core, factors, skip_factor=skip_factor, transpose_factors=transpose_factors))

``````

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