function display_digit(img,varargin)
% FORMAT display_digit(img,[Lab,TruLab])
% Displays digits stored as column vectors in matrix img
%
% img   -  256 x n matrix, where each column corresponds to a 16x16 image
% Lab   -  Optional length n-vector of numbers, to be displayed above the
%          image of the digit.
% TruLab-  Optional length n-vector of numbers, true label; "Lab" is
%          then the predicted label.  If Lab(i) ~= TruLab(i), a message is 
%          shown below the image, indicating the true label.
%________________________________________________________________________
% Script:   display_digit.m
% Purpose:  Display gray scale digits with labels
% Author:   Tom Nichols
% Date:     29 Jan 2012
%

if nargin>1
  Lab=varargin{1};
else
  Lab=[];
end
if nargin>2
  TruLab=varargin{2};
else
  TruLab=[];
end
nImg=size(img,2);

clf
% Figure out dimensions of subplots
if (nImg==1)
  N=1;J=1;
else
  N=ceil(sqrt(nImg)*1.75);
  J=ceil(nImg/N);
end

% Loop over images
for i=1:nImg
  subplot(J,N,i);
  imagesc(reshape(img(:,i),[16 16]),[0 150]); axis image
  set(gca,'box','off','Xtick',[],'Ytick',[])
  if ~isempty(Lab)
    title(num2str(Lab(i)),'fontsize',18)
  end
  if ~isempty(TruLab) && TruLab(i)~=Lab(i)
    xlabel(sprintf('(%d)',TruLab(i)),'color',[1 0 0])
  end
end