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The matrix exponential is a matrix function on square matrices analogous to the ordinary exponential function.

14 votes
Accepted

exponential/logarithm for unipotent algebraic groups

This is false in characteristic $p$, no matter how large $p$ is. The counterexample is the group parameterized by $\begin{pmatrix} 1 & t & t^p \\ 0 & 1 & 0 \\ 0 & 0 & 1 \end{pmatrix}$ Its Lie algebr …
Will Sawin's user avatar
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10 votes
Accepted

Integral of the entrywise square of the exponential of a matrix

Inspired strongly by Anthony's answer, here is a formula that works for arbitrary $A$. Let $M$ be the $n^2 \times n^2$ square matrix given by $$M= A \otimes I_n + I_n \otimes A_n$$ i.e. in terms of in …
Will Sawin's user avatar
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9 votes

How to prove this determinant is positive?

The set of matrices of the form $e^{A_1} \dots e^{A_n}$ with $A_1, \dots , A_n$ of this form are a group. This is because it is clearly closed under multiplication and if $A$ is of this form then $-A$ …
Will Sawin's user avatar
  • 148k