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

[mjotex.git] / mjo-common.tex

diff --git a/mjo-common.tex b/mjo-common.tex
index f14b60d8a5a3d70563c8e8055a49516a7ea91a5f..041a1eb604a1bb753ba5b8415098d4f310fecc4d 100644 (file)
--- a/mjo-common.tex
+++ b/mjo-common.tex
@@ -8,6 +8,10 @@
   \usepackage{amsfonts}
 \fi
 
+\ifx\restriction\undefined
+  \usepackage{amssymb}
+\fi
+
 % Place the argument in matching left/right parentheses.
 \newcommand*{\of}[1]{ \left({#1}\right) }
 
@@ -35,15 +39,34 @@
 % A seven-tuple of things.
 \newcommand*{\septuple}[7]{ \left({#1},{#2},{#3},{#4},{#5},{#6},{#7}\right) }
 
-% The direct sum of two things.
-\newcommand*{\directsum}[2]{ {#1}\oplus{#2} }
-
-% The direct sum of three things.
-\newcommand*{\directsumthree}[3]{ \directsum{#1}{\directsum{#2}{#3}} }
+% The "least common multiple of" function. Takes a nonempty set of
+% things that can be multiplied and ordered as its argument. Name
+% chosen for synergy with \gcd, which *does* exist already.
+\newcommand*{\lcm}[1]{ \operatorname{lcm}\of{{#1}} }
+\ifdefined\newglossaryentry
+  \newglossaryentry{lcm}{
+    name={\ensuremath{\lcm{X}}},
+    description={the least common multiple of the elements of $X$},
+    sort=l
+  }
+\fi
 
 % The factorial operator.
 \newcommand*{\factorial}[1]{ {#1}! }
 
+% Restrict the first argument (a function) to the second argument (a
+% subset of that functions domain). Abused for polynomials to specify
+% an associated function with a particular domain (also its codomain,
+% in the case of univariate polynomials).
+\newcommand*{\restrict}[2]{{#1}{\restriction}_{#2}}
+\ifdefined\newglossaryentry
+  \newglossaryentry{restriction}{
+    name={\ensuremath{\restrict{f}{X}}},
+    description={the restriction of $f$ to $X$},
+    sort=r
+  }
+\fi
+
 %
 % Product spaces
 %
@@ -134,9 +157,6 @@
 }
 
 
-\newcommand*{\directsummany}[3]{ \binopmany{\bigoplus}{#1}{#2}{#3} }
-
-
 % The four standard (UNLESS YOU'RE FRENCH) types of intervals along
 % the real line.
 \newcommand*{\intervaloo}[2]{ \left({#1},{#2}\right) } % open-open