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    Metadata details:
    filename: sshopm.m
    path of file: ./repos/imtsl/libs/tensor_toolbox_2.5
    
    the code of the file until where you have to start completion: function [lambda,x,flag,its,x0,trace,tracex] = sshopm(A,varargin)
%SSHOPM Shifted power method for finding a real eigenpair of a real tensor.
%
%   [LAMBDA,X]=SSHOPM(A) finds an eigenvalue (LAMBDA) and eigenvector (X)
%   for the real tensor A such that Ax^{m-1} = lambda*x.
%

    
function [lambda,x,flag,its,x0,trace,tracex] = sshopm(A,varargin)
%SSHOPM Shifted power method for finding a real eigenpair of a real tensor.
%
%   [LAMBDA,X]=SSHOPM(A) finds an eigenvalue (LAMBDA) and eigenvector (X)
%   for the real tensor A such that Ax^{m-1} = lambda*x.
%
%   [LAMBDA,X]=SSHOPM(A,parameter,value,...) can specify additional
%   parameters as follows: 
% 
%     'Shift'    : Shift in the eigenvalue calculation (Default: 0)
%     'MaxIts'   : Maximum power method iterations (Default: 1000)
%     'Start'    : Initial guess (Default: normal random vector)
%     'Tol'      : Tolerance on norm of change in |lambda| (Default: 1e-16)
%     'Concave'  : Treat the problem as concave rather than convex.
%                  (Default: true for negative shift; false otherwise.)
%     'Display'  : Display every n iterations (Default: -1 for no display)
%
%   [LAMBDA,X,FLAG]=SSHOPM(...) also returns a flag indicating convergence.
%
%      FLAG = 0  => Succesfully terminated 
%      FLAG = -1 => Norm(X) = 0
%      FLAG = -2 => Maximum iterations exceeded
%
%   [LAMBDA,X,FLAG,IT]=SSHOPM(...) also returns the number of iterations.
%
%   [LAMBDA,X,FLAG,IT,X0]=SSHOPM(...) also returns the intial guess.
%
%   [LAMBDA,X,FLAG,IT,X0,TRACE]=SSHOPM(...) also returns a trace of the
%   lambda values at each iteration.
%
%   REFERENCE: T. G. Kolda and J. R. Mayo, Shifted Power Method for
%   Computing Tensor Eigenpairs, SIAM Journal on Matrix Analysis and
%   Applications 32(4):1095-1124, October 2011 (doi:10.1137/100801482)    
%
%   See also SSHOPMC, TENSOR, SYMMETRIZE, ISSYMMETRIC.
%
%MATLAB Tensor Toolbox.
%Copyright 2012, Sandia Corporation.

% This is the MATLAB Tensor Toolbox by T. Kolda, B. Bader, and others.
% http://www.sandia.gov/~tgkolda/TensorToolbox.
% Copyright (2012) 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 on A
P = ndims(A);
N = size(A,1);

if ~issymmetric(A)
    error('Tensor must be symmetric.')
end