Remove space after math environment

Question

After and before a math environment like $$1+1$$ a space is created to separate text from math. But if the math environment has no text after it, an unnecesary space is created like in:

lorem ipsum dolor
$$1+1$$
\section{new section}

The unnecesary space is in between $$1+1$$ and \section.

This can be due to I am using parskip to automatically go to another paragraph by pressing enter. I am wondering if this last space could be removed manually or automatically.

Answer 1

I do not follow your claim that

The[re is] unnecesary space ... between $$1+1$$ and \section.

First off, let's posit that you should never use $$ in a LaTeX document to initiate and terminate single-line display math mode. Instead, do use \[ and \]. For more information on this subject, please see the posting Why is \[ ... \] preferable to $$ ... $$?

Second, please compare the amounts of vertical whitespace in the following two-column example:

The only difference is the use of \[ ... \] on the left and of $ ... $, i.e., of inline math mode within text mode, on the right. Observe that the vertical distance between the math expressions and the subsequent section headers is the same. This vertical distance is controlled by the specification of the \section command, not by whether the final preceding material is typeset in text mode or display-math mode.

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Addendum: If one were to modify the preceding example by loading the parskip package, there would be more whitespace at the first paragraph break, i.e., between ldkjfal;sdfkj and $1+1=2$. However, the vertical space between the math-y expressions and the subsequent sectioning header lines would be the same as in the example shown above. Conclusion: LaTeX does not insert "unnecessary" space between a displayed equation and a subsequent \section directive.

\documentclass[twocolumn]{article}
\begin{document}

% left-hand column:

ldkjfal;sdfkj
\[
1+1=2
\]

\section{A new section}

\newpage % force a column break

% right-hand column:

ldkjfal;sdfkj

$1+1=2$

\section{Another new section}

\end{document}