Machine Learning displayData.m

    function [h, display_array] = displayData(X, example_width)
    %DISPLAYDATA Display 2D data in a nice grid
    %   [h, display_array] = DISPLAYDATA(X, example_width) displays 2D data
    %   stored in X in a nice grid. It returns the figure handle h and the 
    %   displayed array if requested.
    
    % Set example_width automatically if not passed in
    if ~exist('example_width', 'var') || isempty(example_width) 
    example_width = round(sqrt(size(X, 2)));
    end
    
    % Gray Image
    colormap(gray);
    
    % Compute rows, cols
    [m n] = size(X);
    example_height = (n / example_width);
    
    % Compute number of items to display
    display_rows = floor(sqrt(m));
    display_cols = ceil(m / display_rows);
    
    % Between images padding
    pad = 1;
    
    % Setup blank display
    display_array = - ones(pad + display_rows * (example_height + pad), ...
                       pad + display_cols * (example_width + pad));
    
    % Copy each example into a patch on the display array
    curr_ex = 1;
    for j = 1:display_rows
    for i = 1:display_cols
        if curr_ex > m, 
            break; 
        end
        % Copy the patch
    
        % Get the max value of the patch
        max_val = max(abs(X(curr_ex, :)));
        display_array(pad + (j - 1) * (example_height + pad) + (1:example_height), ...
                      pad + (i - 1) * (example_width + pad) + (1:example_width)) = ...
                        reshape(X(curr_ex, :), example_height, example_width) / max_val;
        curr_ex = curr_ex + 1;
    end
    if curr_ex > m, 
        break; 
    end
    end
    
    % Display Image
    h = imagesc(display_array, [-1 1]);
    
    % Do not show axis
    axis image off
    
    drawnow;
    
    end