function y = symconv(x, h, type, f1, keep)
if strcmp(type, 'row')
     y = conv2(x,h);
     y = y(: , 1:2:end);
     y = y(: , f1/2 + 1:f1/2 + keep(2));
else
     y= conv2(x , h');
     y = y(1:2:end, : );
     y = y(f1/2 + 1:f1/2 + keep(1), :);
end