Is Partitioning a Graph into Two Sets a Cut Set?

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  • Thread starter Ackbach
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    2016
In summary, a cut set in graph theory is a set of edges that, when removed, disconnects the graph into two or more subgraphs. It is not always possible to partition a graph into two sets, but for many graphs, this can be done using a cut set. A graph can have more than one cut set, and finding a cut set is closely related to graph coloring. This concept has many real-world applications, such as in network optimization and data clustering.
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Ackbach
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Here is this week's POTW:

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Show that if the vertex set of a connected graph $G=(V,E)$ is partitioned into two nonempty sets $X$ and $Y$, the disconnecting set $F=(X,Y)$ consisting of all edges of $G$ joining vertices in $X$ and vertices in $Y$ is a cut set if the subgraph $G'=(V,E-F)$ has exactly two components.

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Remember to read the http://www.mathhelpboards.com/showthread.php?772-Problem-of-the-Week-%28POTW%29-Procedure-and-Guidelines to find out how to http://www.mathhelpboards.com/forms.php?do=form&fid=2!
 
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No one answered this week's POTW, which is taken from the Schaum's Outlines Graph Theory book, by Balakrishnan. Here is the book's answer:

Suppose $F=(X,Y)$ is not a cut set. Then there is a proper subset $F'$ of $F$ that is a cut set. Let $e=\{x,y\}$ in an edge in $F-F'$ joining vertex $x$ in $X$ and vertex $y$ in $Y$. If $v$ is any vertex in $X$, there is a path joining $v$ and $x$ consisting of vertices from $X$ only. Likewise, if $w$ is any vertex in $Y$, there is a path joining $w$ and $y$ consisting of vertices from $Y$ only. Thus the deletion of all the edges belonging to $F'$ from the graph will not make it disconnected. This is a contradiction since $F'$ is a disconnecting set.
 

FAQ: Is Partitioning a Graph into Two Sets a Cut Set?

What is a cut set in graph theory?

A cut set in graph theory is a set of edges that, when removed, disconnects the graph into two or more subgraphs. This means that the cut set separates the graph into two distinct sets of vertices.

Is partitioning a graph into two sets always possible?

No, it is not always possible to partition a graph into two sets. Some graphs, such as complete graphs, cannot be partitioned into two sets using a cut set. However, many graphs can be partitioned into two sets using a cut set, and this is a useful concept in graph theory.

Can a graph have more than one cut set?

Yes, a graph can have more than one cut set. In fact, there can be multiple ways to partition a graph into two sets using cut sets. The number of possible cut sets in a graph depends on the size and structure of the graph.

How is partitioning a graph into two sets related to graph coloring?

Partitioning a graph into two sets using a cut set is closely related to graph coloring. In fact, every cut set in a graph corresponds to a valid graph coloring with two colors. This means that finding a cut set in a graph is equivalent to finding a two-coloring for that graph.

Can partitioning a graph into two sets using a cut set be applied to real-world problems?

Yes, partitioning a graph into two sets using a cut set has many real-world applications. For example, it can be used in network optimization, data clustering, and classification problems. It is also a fundamental concept in graph algorithms and can be used to solve a variety of graph-related problems.

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