Paul Balduf<p>Currently, I'm working on a problem in <a href="https://mathstodon.xyz/tags/quantum" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>quantum</span></a> field theory where we use <a href="https://mathstodon.xyz/tags/FeynmanIntegral" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>FeynmanIntegral</span></a> s. These integrals are depicted by graphs, and they can be divergent when a graph has too many edges for a given number of vertices. The task is to identify all subgraphs that are divergent. This is a coproduct: It produces multiple terms, and each term is a list of 2 elements. The first element is one or multiple divergent subgraphs, and the second element is the remainder. It is surprising how many terms the coproduct has even for small graphs. For my example, even if the red graph is rather small, there are already 15 combinations of divergent subgraphs. To compute a physically sensible result, one needs to sum over all original graphs, and subtract all these combinations of subgraphs. <a href="https://mathstodon.xyz/tags/physics" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>physics</span></a> <a href="https://mathstodon.xyz/tags/research" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>research</span></a></p>