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    filename: ttm.m
    path of file: ./repos/tensor_toolbox/@ktensor
    
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%TTM Tensor times matrix for ktensor.
%
%   Y = TTM(X,A,N) computes the n-mode product of the ktensor X with a
%   matrix A; i.e., X x_N A.  The integer N specifies the dimension
%   (or mode) of X along which A should be multiplied.  If size(A) =
%   [J,I], then X must have size(X,N) = I.  The result will be a
%   ktensor of the same order and size as X except that size(Y,N) = J.
%
%   Y = TTM(X,{A,B,C,...}) computes the n-mode product of the ktensor
%   X with a sequence of matrices in the cell array.  The n-mode
%   products are computed sequentially along all dimensions (or modes)
%   of X. The cell array contains ndims(X) matrices.
%
%   Y = TTM(X,{A,B,C,...},DIMS) computes the sequence tensor-matrix
%   products along the dimensions specified by DIMS.
%
%   Y = TTM(...,'t') performs the same computations as above except
%   the matrices are transposed.
%
%   Examples
%   X = ktensor({rand(5,2),rand(3,2),rand(4,2),rand(2,2)});
%   A = rand(4,5); B = rand(4,3); C = rand(3,4); D = rand(3,2);
%   Y = ttm(X, A, 1)         %<-- computes X times A in mode-1
%   Y = ttm(X, {A,B,C,D}, 1) %<-- same as above
%   Y = ttm(X, A', 1, 't')   %<-- same as above
%   Y = ttm(X, {A,B,C,D}, [1 2 3 4]) %<-- 4-way multiply
%   Y = ttm(X, {D,C,B,A}, [4 3 2 1]) %<-- same as above
%   Y = ttm(X, {A,B,C,D})            %<-- same as above
%   Y = ttm(X, {A',B',C',D'}, 't')   %<-- same as above
%   Y = ttm(X, {C,D}, [3 4])     %<-- X times C in mode-3 & D in mode-4
%   Y = ttm(X, {A,B,C,D}, [3 4]) %<-- same as above
%   Y = ttm(X, {A,B,D}, [1 2 4])   %<-- 3-way multiply
%   Y = ttm(X, {A,B,C,D}, [1 2 4]) %<-- same as above
%   Y = ttm(X, {A,B,D}, -3)        %<-- same as above
%   Y = ttm(X, {A,B,C,D}, -3)      %<-- same as above
%
%   See also KTENSOR, KTENSOR/TTV, TENSOR/TTM.
%
%MATLAB Tensor Toolbox.
%Copyright 2015, Sandia Corporation.

% This is the MATLAB Tensor Toolbox by T. Kolda, B. Bader, and others.
% http://www.sandia.gov/~tgkolda/TensorToolbox.
% Copyright (2015) Sandia Corporation. Under the terms of Contract
% DE-AC04-94AL85000, there is a non-exclusive license for use of this
% work by or on behalf of the U.S. Government. Export of this data may
% require a license from the United States Government.
% The full license terms can be found in the file LICENSE.txt



    
function X = ttm(X,V,varargin)
%TTM Tensor times matrix for ktensor.
%
%   Y = TTM(X,A,N) computes the n-mode product of the ktensor X with a
%   matrix A; i.e., X x_N A.  The integer N specifies the dimension
%   (or mode) of X along which A should be multiplied.  If size(A) =
%   [J,I], then X must have size(X,N) = I.  The result will be a
%   ktensor of the same order and size as X except that size(Y,N) = J.
%
%   Y = TTM(X,{A,B,C,...}) computes the n-mode product of the ktensor
%   X with a sequence of matrices in the cell array.  The n-mode
%   products are computed sequentially along all dimensions (or modes)
%   of X. The cell array contains ndims(X) matrices.
%
%   Y = TTM(X,{A,B,C,...},DIMS) computes the sequence tensor-matrix
%   products along the dimensions specified by DIMS.
%
%   Y = TTM(...,'t') performs the same computations as above except
%   the matrices are transposed.
%
%   Examples
%   X = ktensor({rand(5,2),rand(3,2),rand(4,2),rand(2,2)});
%   A = rand(4,5); B = rand(4,3); C = rand(3,4); D = rand(3,2);
%   Y = ttm(X, A, 1)         %<-- computes X times A in mode-1
%   Y = ttm(X, {A,B,C,D}, 1) %<-- same as above
%   Y = ttm(X, A', 1, 't')   %<-- same as above
%   Y = ttm(X, {A,B,C,D}, [1 2 3 4]) %<-- 4-way multiply
%   Y = ttm(X, {D,C,B,A}, [4 3 2 1]) %<-- same as above
%   Y = ttm(X, {A,B,C,D})            %<-- same as above
%   Y = ttm(X, {A',B',C',D'}, 't')   %<-- same as above
%   Y = ttm(X, {C,D}, [3 4])     %<-- X times C in mode-3 & D in mode-4
%   Y = ttm(X, {A,B,C,D}, [3 4]) %<-- same as above
%   Y = ttm(X, {A,B,D}, [1 2 4])   %<-- 3-way multiply
%   Y = ttm(X, {A,B,C,D}, [1 2 4]) %<-- same as above
%   Y = ttm(X, {A,B,D}, -3)        %<-- same as above
%   Y = ttm(X, {A,B,C,D}, -3)      %<-- same as above
%
%   See also KTENSOR, KTENSOR/TTV, TENSOR/TTM.
%
%MATLAB Tensor Toolbox.
%Copyright 2015, Sandia Corporation.

% This is the MATLAB Tensor Toolbox by T. Kolda, B. Bader, and others.
% http://www.sandia.gov/~tgkolda/TensorToolbox.
% Copyright (2015) Sandia Corporation. Under the terms of Contract
% DE-AC04-94AL85000, there is a non-exclusive license for use of this
% work by or on behalf of the U.S. Government. Export of this data may
% require a license from the United States Government.
% The full license terms can be found in the file LICENSE.txt



%%%%%%%%%%%%%%%%%%%%%%
%%% ERROR CHECKING %%%
%%%%%%%%%%%%%%%%%%%%%%

% Check the number of arguments
if (nargin < 2)
    error('TTM requires at least two arguments.');
end