Graph operations and cordiality.
Maged Zakaria Youssef, E. A. Elsakhawi · 2010
In this paper, we show that the disjoint union of two cordial graphs one of them is of even size is cordial and the join of two cordial graphs both are of even size or one of them is of even size and one of them is of even order is cordial. We also show that Cm ∪ Cn is cordial if and only if m+n ≡ / 2 (mod 4) and mCn is cordial if and only if mn ≡ / 2 (mod 4) and for m, n ≥ 3, Cm + Cn is cordial if and only if (m, n) ≠ (3, 3) and {m,n} ≡ / {0, 2} (mod 4). Finally, we discuss the cordiality of knP.