On Tades of Disjoint Union of Some Graphs

A. Lourdusamy1, F. Joy Beaula2, F. Patrick1
1Department of Mathematics, St. Xavier’s College (Autonomous), Palayamkottai-627002, India.
2Center: PG and Research Department of Mathematics, St. Xavier’s College (Autonomous), Palayamkottai-627002, Manonmaniam Sundaranar University, Abisekapatti-627012, Tamilnadu, India.

Abstract

Consider a total labeling ξ of a graph G. For every two different edges e and f of G, let wt(e)wt(f) where weight of e=xy is defined as wt(e)=|ξ(e)ξ(x)ξ(y)|. Then ξ is called edge irregular total absolute difference k-labeling of G. Let k be the minimum integer for which there is a graph G with edge irregular total absolute difference labeling. This k is called the total absolute difference edge irregularity strength of the graph G, denoted tades(G). We compute tades of SCn, disjoint union of grid and zigzag graph.

Keywords: Total absolute difference edge irregularity strength, Edge irregularity strength, Zigzag graph, Grid graph, Staircase graph

1. Introduction and Motivation

Chartrand et al. [1] introduced irregularity strength and irregular assignments of a graph in 1988. The other kind of total labeling the total edge irregularity strength of a graph was studied by Baca et al. [2]: Consider a graph G=(V,E). A labeling ξ:VE{1,2,,k} is called an edge irregular total k-labeling if for every pair of distinct edges uv and xy, ξ(u)+ξ(v)+ξ(uv)ξ(x)+ξ(y)+ξ(xy). If a graph G admits an edge irregular total k-labeling and k is minimum then G is said to have a total edge irrgularity strength denoted by tes(G). The results about the tes(G) can be found in [3,4,5,6,7,8,9,10].

Ramalakshmi and Kathiresan introduced the total absolute difference edge irregularity strength of graphs to lower edge weights, using tes(G) and graceful labeling. Consider a total labeling ξ of a graph G. For every two different edges e and f of G, let wt(e)wt(f) where weight of e=xy is defined as wt(e)=|ξ(e)ξ(x)ξ(y)|. Then ξ is called edge irregular total absolute difference k-labeling of G. Let k be the minimum integer for which there is a graph G with edge irregular total absolute difference labeling. This k is called the total absolute difference edge irregularity strength of the graph G, denoted tades(G).

Lourdusamy et al. [11] determined the total absolute difference edge irregular strength for snake related graphs, wheel related graphs, lotus inside the circle and double fan graph. Also, they obtained the tades of Tp-tree related graphs [12]. Lourdusamy et al. [13] discussed the tades of super subdivision of certain families of graphs and corona graphs. Also, they obtained the tades of transformed tree and path related graphs [14]. Here, we discuss the tades of staircase graph, disjoint union of zigzag and grid graphs.

Theorem 1. [15] For a graph G=(V,E), we have |E|2tades(G)|E|+1.

2. Main Results

In this section, we compute the exact value of total absolute difference edge irregularity strength of staircase graph.

Theorem 2. For SCn, the total absolute difference edge irregularity strength is tades(SCn)=n(n+3)2.

Proof. Let k=n(n+3)2. Let V(SCn)={ar,s:r=0,1,0sn}{ar,s:2rn,r1sn} and E(SCn)={ar,sar+1,s:r=0,0sn}{ar,sar+1,s:1rn1,rsn}{ar,sar,s+1:r=0,1,0sn1}{ar,sar,s+1:2rn,r1sn1}. Note that |V(SCn)|=12(n+1)(n+2)+n and |E(SCn)|=n(n+3).

From Theorem 1, tades(SCn)k. To complete the proof we show that tades(SCn)k. We define a, k-labeling ξ:V(SCn)E(SCn){1,2,k} as follows:
ξ(ar,0)=1,r=0,1;
For 1sn
ξ(a0,s)=s2+3s2s2;
Case 1. s is odd
Let 1sn and s is odd .
Fix ξ(a1,s)=s2+3s2s2.
Let 2rn, r1sn and s is odd.
Fix ξ(ar,s)={s2+3s2s2+r12 if  r is odds2+3s2s2+r2if r is even ;
Case 2. s is even
Let 1sn and s is even.
Fix ξ(a1,s)=s2+3s2s2+1.
Let 2rn, r1sn and s is even.
Fix ξ(ar,s)={s2+3s2s2+r+12if r is odds2+3s2s2+r2if r is even .
We fix the edge labels as follows:
ξ(a0,0a1,0)=2;
ξ(a0,0a0,1)=2;
ξ(a1,0a1,1)=1;
ξ(a0,sa1,s)=1 , for 1sn;
ξ(ar,sar+1,s)=1, for 1rn1 and rsn;
ξ(ar,sar,s+1)=1, for r=0,1 and 1sn1;
ξ(ar,sar,s+1)=1, for 2rn and r1sn1.
We then have the weight of the edges as follows:
wt(a0,0a1,0)=0;
wt(a0,0a0,1)=1;
wt(a1,0a1,1)=2;
wt(a0,sa1,s)=s2+2s for 1sn;
wt(ar,sar+1,s)=s2+2s+r, for 1rn1 and rsn;
wt(ar,sar,s+1)=s2+3s+1, for r=0,1 and 1sn1;
wt(ar,sar,s+1)=s2+3s+r+1, for 2rn and r1sn1.
Hence ξ is total absolute difference edge irregular k-labeling with k=n(n+3)2 as the weights for the edges are different. 

3. Disjoint Union of Zigzag Graph

In this section, we compute the exact value of total absolute difference edge irregularity strength of disjoint union of zigzag graphs j=1pZnjmj with nj2  and mj2.

Theorem 3. For any integer nj2, mj2, tades(j=1pZnjmj)=j=1p(nj1)(2mj1)2.

Proof. Let k=j=1p(nj1)(2mj1)2. The disjoint union j=1pZnjmj of zigzag graphs Znm is defined to be a graph with vertex set V(j=1pZnjmj)={ai,sj:1inj,1smj,1jp} and the edge set E(j=1pZnjmj)={ai,sjai+1,sj:1inj1,1smj,1jp}{ai,sjai1,s+1j:1inj,1smj1,1jp}. The disjoint union of zigzag graphs j=1pZnjmj has j=1pnjmj vertices and j=1p(nj1)(2mj1) edges. Based on Theorem 1, we have tades(j=1pZnjmj)j=1p(nj1)(2mj1)2.

We define ξ as follows:
for 1inj, 1smj and 1jp1,
ξ(ai,sj)=r2+(s1)(nj1)+i+12((1)r+1)2 where r=q=1j1(nq1)(2mq1);
for 1inp, 1smp1 and r=q=1p1(nq1)(2mq1),
ξ(ai,sp)=r2+(s1)(np1)+i+12((1)r+1)2 ;
ξ(ai,mpp)={r2+(mp1)(np1)+i+12((1)r+1)2if 1inp1k if  i=np ;
ξ(ai,sjai+1,sj)=2, for 1inj1, 1smj and 1jp1;
ξ(ai,spai+1,sp=2, for 1inp1, 1smp1;
ξ(ai,mppai+1,mpp)=2,  for 1inp2;
ξ(anp1,mppanp,mpp)={1if |E(j=1pZnjmj)| iseven2if |E(j=1pZnjmj)| is odd;
ξ(ai1,s+1jai,sj)=2,  for 2inj, 1smj1 and 1jp.
We now arrive at the weight of the edges:
for 1inj1, 1smj, 1jp and r=q=1j1(nq1)(2mq1),
wt(ai,sjai+1,sj)=2r2+2(s1)(nj1)+i+12((1)r+1)2;
for 1inj, 1smj1, 1jp and r=q=1j1(nq1)(2mq1),
wt(ai,sjai1,s+1j)=2r2+(2s1)(nj1)+i+12((1)r1)3.
It is clear that, the labels for vertices and edges receive values are not more than k. Also we see that the weights for the edges are all distinct. Hence tades(j=1pZnjmj)=j=1p(nj1)(2mj1)2

Illustration for tades of Z54Z65Z46Z37 is shown in Figure 3.

4. Disjoint Union of Grid Graph

In this section, we compute the exact value of total absolute difference edge irregularity strength of disjoint union of grid graphs j=1pZnjmj with nj,mj2.

Theorem 4. For any integer nj,mj2 and 1jp, tades(j=1pGnj,mj)=j=1p(2njmjmjnj)2.

Proof. Let k=j=1p(2njmjmjnj)2. We define disjoint union j=1pGnj,mj of grid graphs Gn,m as follows:
Let V(j=1pGnj,mj)={ai,sj:1inj,1smj,1jp}. Let E(j=1pGnj,mj)={ai,sj,ai+1,sj:1inj1,1smj,1jp}{ai,sj,ai,s+1j:1inj,1smj1,1jp}. From Theorem 1, tades(j=1pGnj,mj)j=1p(2njmjmjnj)2. Now we prove the converse part.

Let us define ξ:V(j=1pGnj,mj)E(j=1pGnj,mj){1,2,,j=1p(2njmjmjnj)2} as follows:
for 1inj, 1smj and 1jp1,
ξ(ai,sj)={t2+s12(2nj1)+i+12((1)t+1)2 if s is oddt2+nj(s1)s2+i+12((1)t+1)2 if s is even ;
where t=q=1j12nqmqmqnq
for 1inp,1smp1 and t=q=1p12nqmqmqnq
ξ(ai,sp)={t2+s12(2np1)+i+12((1)t+1)2 if s is oddt2+np(s1)s2+i+12((1)t+1)2 if s is even ;
for 1inp1,
ξ(ai,mpp)={t2+mp12(2np1)+i+12((1)t+1)2 if s is oddt2+np(mp1)mp2+i+12((1)t+1)2 if s is even ;
ξ(anp,mpp)=k;
ξ(ai,sjai+1,sj)=2, for 1inj1, 1smj and 1jp1;
ξ(ai,spai+1,sp)=2, for 1inp1, 1smp1;
ξ(ai,mppai+1,mpp)=2,  for 1inp2;
ξ(anp1,appanp,mpp)={1if |E(j=1pGnj,mj)| iseven2if |E(j=1pGnj,mj)| is odd;
ξ(ai,sjai,s+1j)=2,  for 2inj, 1smj1 and 1jp.
Below we arrive at the weight of the edges. for 1inj1, 1smj, 1jp and t=q=1j12nqmqmqnq,
wt(ai,sjai+1,sj)={2t2+(s1)(2nj1)+i+12((1)t+1)2 s is odd2t2+(s1)2njs+i+1+12((1)t+1)2 s is even;
for 1inj, 1smj1, 1jp and t=k=1j12njmjmjnj,
wt(ai,sjai,s+1j)=2t2+(2s1)njs+i+12((1)t+1)2.
It is clear that, the labels for vertices and edges receive values are not more than k. Also we see that the weights for the edges are all distinct. Hence tades(j=1pGnj,mj)=j=1p(2njmjmjnj)2. 

Illustration for tades of G6,7G5,6G4,5 is shown in Figure 5.

Conflict of Interest

The authors declare no conflict of interests.

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