Modular Representation Theory - Example

Example

Finding a representation of the cyclic group of two elements over F2 is equivalent to the problem of finding matrices whose square is the identity matrix. Over every field of characteristic other than 2, there is always a basis such that the matrix can be written as a diagonal matrix with only 1 or −1 occurring on the diagonal, such as


\begin{bmatrix}
1 & 0\\
0 & -1
\end{bmatrix}.

Over F2, there are many other possible matrices, such as


\begin{bmatrix}
1 & 1\\
0 & 1
\end{bmatrix}.

Over an algebraically closed field of positive characteristic, the representation theory of a finite cyclic group is fully explained by the theory of the Jordan normal form. Non-diagonal Jordan forms occur when the characteristic divides the order of the group.

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