how can I extract from iddata to matrix to have calculation? pe function

load dryer2

data=iddata(y2,u2,1);

sys=arx(data,[3 3 1])

err=pe(sys,data);

pe(sys,data);

Now it plots the errors. but i want to extract that errors to one array like matrix "err" to do calculation on it. for example find absolute sum of them

thanks