mjo-linear_algebra.tex: update a comment before abusing notation.

[mjotex.git] / mjo-linear_algebra.tex

diff --git a/mjo-linear_algebra.tex b/mjo-linear_algebra.tex
index d493b9cce5bd047eeb940a972128a6cf7198d261..a534523765ef1fd20f7729af25836bb2075fcd3e 100644 (file)
--- a/mjo-linear_algebra.tex
+++ b/mjo-linear_algebra.tex
@@ -51,6 +51,11 @@
 % The trace of an operator.
 \newcommand*{\trace}[1]{ \operatorname{trace}\of{{#1}} }
 
+% The diagonal matrix whose only nonzero entries are on the diagonal
+% and are given by our argument. The argument should therefore be a
+% vector or tuple of entries, by convention going from the top-left to
+% the bottom-right of the matrix.
+\newcommand*{\diag}[1]{\operatorname{diag}\of{{#1}}}
 
 % The "rank" of its argument, which is context-dependent. It can mean
 % any or all of,
@@ -146,7 +151,9 @@
 
 % The space of complex Hermitian n-by-n matrices. Does not reduce to
 % merely "H" when n=1 since H^{n} does not mean an n-fold cartesian
-% product of H^{1}.
+% product of H^{1}. The field may also be given rather than assumed
+% to be complex; for example \Hn[3]\of{\mathbb{O}} might denote the
+% 3-by-3 Hermitian matrices with octonion entries.
 \newcommand*{\Hn}[1][n]{ \mathcal{H}^{#1} }
 \ifdefined\newglossaryentry
   \newglossaryentry{Hn}{