function r = plus(p,q)
% POLYNOM/PLUS Implement p + q for polynoms.
p = polynom(p);
q = polynom(q);
k = length(q.c) - length(p.c);
% if k is positive then zeros need to be added to p 
% if k is negative then zeros need to be added to q
% note: if the second argument to ZEROS is negative then an
% empty matrix is formed
r = polynom([zeros(1,k) p.c] + [zeros(1,-k) q.c]);