% transforms a matrix into a tensor with the specified single-plane dimension;
% also returns the dimensions of the new tensor

function [t,tdim] = tmat2ten(a,d)

if isempty(a),
  t = [];
else
  if d == 1,
    tdim = [1 size(a)];
    % 'i' matrices are stored as row vectors
    a = a(:)';
  elseif d == 2,
    tdim = [size(a,1) 1 size(a,2)];
  elseif d == 3,
    tdim = [size(a) 1];
  else
    error('d must be between 1 and 3')
  end

  t = tzeros(tdim);
  t(:,1:(size(t,2)-1)) = a;
end