# What is a K-connected Graph?

A k-connected graph is a graph theory that describes how connected or robust a graph is. In a chart, the network alludes to how well vertices are associated. A diagram is viewed as k-associated if it stays associated after eliminating any k-1 vertices (along with the occurrence of the edge to those vertices).

A chart G is supposed to be k-associated if there are essentially k various ways between any two vertices in G, and eliminating not exactly k vertices won't make the diagram separate. In other words, no set of vertices fewer than k may divide the graph into two disconnected components.

A graph G is said to be k-connected if:

i) There are more than k vertices.

ii) There are k internally disjoint pathways between each pair of vertices in G. Internally disconnected pathways have no common vertices (save the endpoints).

### Example:

1. Connected Graph:

Removing 0 vertices maintains the graph linked.

2. Associated Chart (Biconnected Diagram)

The expulsion of one vertex might separate the chart; however, there is currently something like one way between any two vertices.

3. Associated Diagram:

Even though eliminating two vertices might disengage the diagram, there are currently no less than three inside disjoint pathways between any two vertices.

### Applications:

K-associated diagrams are helpful in different spaces, including network plans, unwavering quality examinations, lenient framework shortcomings, and correspondence organizations. A chart with a higher k-network is stronger and shortcomings lenient, making it less inclined to hub disappointments.

### Properties

i) Definition:

A graph G is k-connected if and only if:

- G has over k vertices.

- There are k internally disjoint pathways between any two vertices u and v in G.

ii) Connection and Cut Vertices:

A graph's cut vertex (also known as an articulation point) is removed to increase the number of connected components. Cut vertices are especially important in the context of k-connected networks. A chart's cut vertex (or verbalization point) is taken out to expand the number of associated parts.

A graph is considered to be one-connected only if it does not have any cut vertices. In a 1-associated diagram, there are no cut vertices, which implies that eliminating a solitary vertex doesn't separate the organization.

- A chart is 2-associated if and provided that it contains no cut vertices and stays associated following the expulsion of any single vertex.

- A chart is k-associated if and provided that it has no cut set with a size not exactly k.

iii) Menger's Theorem on Vertices:

Menger's Hypothesis portrays the connection between a diagram's connectedness and irregular pathways between vertices.

For each two non-nearby vertices u and v in a chart G, the negligible number of vertices (vertex cut) expected to detach you and v is equivalent to the best number of inside disjoint ways associating them.

iv) K-connectedness and Cut Sets:

A k-connected graph cannot be disconnected by removing any set of fewer than k vertices because the smallest vertex cut set-the set of vertices whose removal disconnects the graph-is k.

v) Implications for Network Design:

- Fault Tolerance

K-connected graphs are critical for creating fault-tolerant networks.

Higher k-connectivity means greater tolerance to node or link failures while maintaining overall network connectivity.

- Robustness:

Networks with higher k-connectivity are more robust and resistant to random or purposeful failures.

Robust networks may retain connectivity and communication despite many malfunctions.

- Communication Networks:

Maintaining a specific level of connectedness (k-connectivity) is critical for ensuring continuous and reliable communication.

K-connectedness is useful in designing networks that can endure various failure situations.

vi) Algorithms For K-Connectivity:

1. K-Connectivity is determined as follows:

There are algorithms for determining k-connectivity in a given network. One such method is based on the notion of edge connection.

Edge connectivity is the minimal number of edges required to disconnect a graph. The k-connectivity is then tied to the edge connectivity.

2. Finding vertex-disjoint paths:

To establish k-connectivity, methods can be employed to find k vertex-disjoint pathways between any pair of vertices.

These disjoint paths ensure that the graph is connected even after k-1 vertices are removed.

vii) Planar Graphs with K-Connectivity:

Kuratowski's Theorem.

Kuratowski's Theorem refers to planar graphs and their connection.

A graph is considered planar if it does not have a subgraph that is a subdivision of K? (full graph with 5 vertices) or K?,? (complete bipartite graph with two sets of 3 vertices).

viii) K-Connectivity in Plane Graphs:

K-connectedness is important in the study of planar graphs, particularly for understanding their structural features and the constraints imposed by Kuratowski's Theorem.

## Where is it used?

i) Communication Networks:

The k-connected graph model ensures that communication networks, particularly telecommunications, stay connected even when nodes or links fail. This is critical for ensuring continuous and reliable communication.

ii) Transport Networks:

Using k-connected graphs benefits transportation systems such as road networks and air routes. Ensuring a particular level of connectivity helps prevent regions from being isolated due to infrastructure failure or interruption.

iii) Power grids:

Power distribution networks must be highly reliable to guarantee the uninterrupted distribution of electricity. K-associated charts are utilized to make strong power networks that endure breakdowns while keeping up with availability.

iv) Computer networks:

In computer networks, where reliable data transfer is critical, k-connected graphs create fault-tolerant systems. Ensuring numerous independent pathways between nodes helps to prevent network disruptions caused by hardware or connection issues.

## How do you identify a K-connected graph?

1. Check Vertex and Edge connection:

Compute the graph's vertex and edge connection. For a graph to be k-connected, both must be equal or greater than k.

To get these values, apply techniques or theorems that calculate vertex or edge connectivity.

2. The Menger Theorem:

Use Menger's Theorem, which specifies a property for k-connected graphs. The smallest number of vertices (vertex cut) that must be removed to disconnect two non-adjacent vertices, u and v, in a k-connected graph equals the maximum number of internally disjoint pathways between them.

3. Identify Vertex-Disjoint Paths:

Determine if there are k internally disjoint paths between any two vertices (u, v).

Use techniques to locate these disjoint pathways and confirm they have no common vertices other than the endpoints.

4. Cut vertices:

- Determine whether the graph has cut vertices. Cut vertices should not appear in a k-connected graph.

- If removing vertices that are fewer than k disconnects the graph, there are cut vertices.

5. Edge-Connectivity Algorithm:

- Use algorithms intended for edge connectivity calculations. A graph's edge connectivity must equal or exceed k to be k-connected.

- Edge-connectivity methods may involve the discovery of edge-disjoint pathways between vertices.

### Pseudo-code

Developing a generic pseudo-code for determining if a particular graph is k-connected entails employing specific algorithms such as Menger's Theorem, network flow algorithms, or other connectivity-based methods. Here is a small pseudo-code sample for a basic technique that uses Menger's Theorem.

The specific algorithm you pick will determine how vertexConnectivity and minVertexCut are implemented. Network flow or maximum flow algorithms such as Ford-Fulkerson may best serve these functions.

Remember that the pseudo-code provided is a high-level representation, and real implementation details may differ depending on the algorithms chosen and the programming language utilized.

## Conclusion

To summarize, k-connected graphs have structural resilience that maintains a minimal level of connectedness inside the graph, as seen by numerous independent pathways between any two vertices. The absence of cut vertices, the application of Menger's Theorem, and the requirement for at least k internally disjoint pathways all contribute to these graphs' resilience and fault tolerance. Whether used in communication networks, transportation systems, or other vital infrastructure, the intrinsic connectedness qualities of k-connected graphs make them invaluable in developing systems that can function even when nodes or edges fail.