Documentation of expandm

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Function Synopsis

MatOut = expandm(MatIn, EXPN)

Help text

 EXPAND a Matrix, utility function

 This function expands a matrix MatIn in both dimensions.
 In the output matrix MatOut each element of MatIn is
 repeated as often as defined in EXPN. The size of MatOut is
 [EXPN(1)*size(MatIn,1), EXPN(2)*size(MatIn,2)].
 This function is used in the GEA Toolbox.

 Input parameters:
    MatIn     - Input Matrix (before expanding)
    EXPN      - Vector of 2 numbers, how often expand in each
                   dimensiom
                EXPN(1): replicate vertically
                EXPN(2): replicate horizontally

 Output parameter:
    MatOut    - Output Matrix (after expanding)

 Example:
    MatIn = [1 2 3
             4 5 6]

    EXPN = [1 2] => MatOut = [1 1 2 2 3 3;
                              4 4 5 5 6 6]

    EXPN = [2 1] => MatOut = [1 2 3;
                              1 2 3;
                              4 5 6;
                              4 5 6]

    EXPN = [3 2] => MatOut = [1 1 2 2 3 3;
                              1 1 2 2 3 3;
                              1 1 2 2 3 3;
                              4 4 5 5 6 6;
                              4 4 5 5 6 6;
                              4 4 5 5 6 6]

 See also: repmat

Cross-Reference Information

Listing of function expandm

% Author:   Hartmut Pohlheim
% History:  13.02.97    file created

function MatOut = expandm(MatIn, EXPN)

% Check input parameters
   if nargin < 2, error('Not enough input parameters!'); end
   if isempty(EXPN), MatOut = MatIn; return; end
   if any(EXPN < 0), error('Expand dimension EXPN must be 1 or 2 numbers > 0!'); end

% If only one number is given, expansion in both dimensions is equal
   if length(EXPN) < 2, EXPN = [EXPN(1), EXPN(1)]; end

% Get size of input matrix
   [MatRows, MatCols] = size(MatIn);

% Calculate expand index
   RowsIx = (1:MatRows);
   ColsIx = (1:MatCols);
   RowsIx = RowsIx(ones(EXPN(1), 1), :);
   ColsIx = ColsIx(ones(EXPN(2), 1), :);

% Create output matrix
   MatOut = MatIn(RowsIx(:), ColsIx(:));


% End of function