function diehist( x )
% plots a normalized histogram of random numbers x drawn from rolling a
% die.
    [h,b] = hist( x, 1:6 );
    h = h/sum(h);   % normalization
    plot( [0 7], [1/6 1/6], 'r', 'linewidth', 3 )
    hold on
    bar( b, h );
    hold off
    set(gca, 'XTick', 1:6 );
    xlim( [ 0, 7 ] );
    xlabel('Eyes');
    ylabel('Probability');
end