function HX = mhalf(X, side)

s = size(X);

if side == 'l'
    sr = round(s(2)/2);
    HX = X(:,1:sr);
elseif side == 'r'
    sr = round(s(2)/2)+1;
    HX = X(:,sr:s(2));
elseif side == 'u'
    sr = round(s(1)/2);
    HX = X(1:sr,:);
elseif side == 'd'
    sr = round(s(1)/2)+1;
    HX = X(sr:s(1),:);
end