In $\LaTeX$, it is not recommended using
$$... $$
for display mode formulas, and
\[...\]
is more recommended. But it seems the latter is not supported on MSE. MSE supports
\begin{equation*}
...
\end{equation*}
, but this is akward for typing. Why \[...\] is not supported?
And I also found \diag, which gives diag in roman font in maths formulas is neither supported.
This answer is meant for testing purposes. (Feel free to edit it if you want to try something related to the issue at hand.)
\[ x^2+y^2=z^2 \] - this works neither in the preview nor in the final post.
[ x^2+y^2=z^2 ]
\\[ x^2+y^2=z^2 \\] - this works both in the preview and in the posted answer.
\[ x^2+y^2=z^2 \]
As mentioned in the question $$ x^2+y^2=z^2 $$ works, too.
$$ x^2+y^2=z^2 $$
If I include $\newcommand{\diag}{\operatorname{diag}}$, then I can use things like $\diag(\lambda_1,\lambda_2,\dots,\lambda_n)$.$\newcommand{\diag}{\operatorname{diag}}$ Here is an example: $\diag(\lambda_1,\lambda_2,\dots,\lambda_n)$.
The scope of \newcommand is now restricted to the post (or the comment) where the definition is used - this behavior used to be different, but this was changed in 2019.
\\[...\\] works. Inspecting the website for MathJax settings shows that \\\\(...\\\\) should also work for inline maths: \\\(a + b = c\\\). I get it to work in the preview, have not tried in an answer
$\endgroup$
Commented
Jan 16 at 13:32
\diagis not supported in LaTeX either: Inline Notation for the Diagonal of a Matrix?. (Unless you load some package defining this command.) On Mathematics you can use$\newcommand{\diag}{\operatorname{diag}}$and after that you can use\diag. For example, it was defined this way in this question: Connecting an almost idempotent complex matrix to a diagonal 1-0 matrix $\endgroup$$$is disallowed in the titles: Using block (displayed) equations in question titles. But from your post it seems that one can bypass this by\[and\]. This was also pointed out here: Circumventing displayed equation ban in titles. $\endgroup$\[...\]behaves differently in the body and in the title. 10k+ users can see this also here (link to a deleted question on the main where I tested the same thing). $\endgroup$