Skip to main content
3 votes
Accepted

De-diagonalize a diagonal matrix back over a subfield from the extension field

This is possible iff the characteristic polynomial of $D$ has coefficients in $K$, or equivalently iff the diagonal entries of $D$ are invariant under the action of the Galois group $G = \text{Gal}(L/...
Qiaochu Yuan's user avatar

Only top scored, non community-wiki answers of a minimum length are eligible