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Questions about the branch of algebra that deals with groups.

11 votes
Accepted

Conjugacy in $GL(n,\mathbb Z)$

The Conjugacy Problem in $\operatorname{GL}(n, \mathbb{Z})$ by Eick, Hofmann and O'Brien gives an algorithm for solving this problem, which has been implemented in Magma.
David Roe's user avatar
  • 506
5 votes

A map from the coinvariants of the dual to the dual of the invariants for a G-module

I will answer the question in the case that $G$ is cyclic or pro-cyclic. Write $t$ for a (topological) generator of $G$. Then we can describe $X^G$ and $X_G$ as the kernel and cokernel of $t-1$: $$ …
David Roe's user avatar
  • 506
13 votes
1 answer
2k views

A map from the coinvariants of the dual to the dual of the invariants for a G-module

Suppose $G$ is a group and $X$ is a $\mathbb{Z}[G]$-module. Recall that the augmentation ideal $I \subset \mathbb{Z}[G]$ is generated by elements of the form $g - 1$ for $g \in G$, the coinvariants a …
David Roe's user avatar
  • 506