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-rw-r--r--FuVar.tex8
1 files changed, 4 insertions, 4 deletions
diff --git a/FuVar.tex b/FuVar.tex
index 62d71f2..61eead8 100644
--- a/FuVar.tex
+++ b/FuVar.tex
@@ -155,7 +155,7 @@ typesetting may trick you into thinking it is rigorous, but really, it is not.
\(\vec{r}\) (with \(|\vec{r}| = 1\)) given by
\[
\frac{\partial f}{\partial\vec{r}}
- = \nabla\vec{r} f = \vec{r} \dotp \grad f
+ = \nabla_\vec{r} f = \vec{r} \dotp \grad f
\]
\end{definition}
@@ -270,13 +270,13 @@ typesetting may trick you into thinking it is rigorous, but really, it is not.
\end{remark}
\begin{method}[Quickly find the eigenvalues of a \(2\times 2\) matrix]
- Let
+ This is a nice trick. For a square matrix \(\mx{H}\), let
\[
m = \frac{1}{2}\tr \mx{H} = \frac{a + d}{2} ,
- \qquad
+ \quad
p = \det\mx{H} = ad - bc ,
\]
- then \(\lambda = m \pm \sqrt{m^2 - p}\).
+ then \(\lambda_{1,2} = m \pm \sqrt{m^2 - p}\).
\end{method}
\begin{method}[Search for a constrained extremum in 2 dimensions]