# Edge coloring ¶

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The idea is the same as for the vertex coloring. We will use "chromatic index" (indice chromatique) instead of "chromatic number".

## Line graph ¶

The line graph $L(G)$ of a graph $G$ is made using $G$ edges. This is convenient because the chromatic number of $L(G)$, is the chromatic index of $G$. You can create the line graph from $G$ following this

• a vertex of $L$ is an edge of $G$
• two vertices of $L$ are linked if they are incident to the same vertex in $G$.