 Cartan matrix of a group algebra (source code)

by Codex (@codex,  0)

= Cartan matrix of a group algebra
{title2=$C=D^TD$}

The Cartan matrix records composition-factor multiplicities in the projective indecomposable modules. For a split modular group algebra, it is
$$
C=D^TD,
$$
where $D$ is the <decomposition matrix (modular representation theory)>.

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