How to get latex to ignore blank lines in equations

Question

When writing equations, I often inadvertently add a empty line. Then latex refuses to compile my tex file until I fill in the empty line. The problem occurs when I mouse in a long formula and the blank line lies below the lines that I can see on my screen without scrolling. This happens to me several times during every latex session.

If latex ignored blank lines (as it ignores blank spaces), this annoying problem would go away.

Instead of a blank line, just use a line with a single % (comment character). It looks similar and avoids the issue. — Steven B. Segletes, Aug 29 '22 at 23:59
Yes, it's annoying, but it's built into TeX itself for a good reason. It's perhaps able to be worked around by coding something in luatex, but it's not going to be changed in the other engines. A good explanation of the reason is given in this answer. This question might be considered a duplicate: Blank lines in an equation and some other similar function — barbara beeton, Aug 30 '22 at 00:05
For the record: In context you can have empty lines in displayed formulas, so it is indeed possible. — mickep, Aug 30 '22 at 06:15
luatex has a primitive counter you can set non zero so that blank lines are not an error, in other engines you could set \let\par\relax in \everydisplay but I probably would not recommended it — David Carlisle, Aug 30 '22 at 06:50

score 6 · Answer 1 · answered Aug 30 '22 at 09:12

In LuaTeX

\suppressmathparerror = 1

Will disable this check at the engine level.

In other engines you could (although it may conflict with other uses) use

\everydisplay{\let\par\relax}
\everymath{\let\par\relax}

To make end of paragraph (\par) be ignored in math mode.

Note as these constructs show, they are not "allowing blank lines in math". Blank lines are never to be regarded as cosmetic source level pretty-printing as they are in some programming laguages. A blank line is reported to the macro layer as \par: an explicit instruction to end a paragraph.

Ending a paragraph mid-display is almost never the semantic intention, so (unlike the similar but completely useless \outer error) there is some logic to making this an error, however ignoring it is a possibility (especially in luatex which has engine level support for disabling this check).

I've heard that the "useless \outer error" can be gotten rid off by \suppressoutererror=1. There is also \suppresslongerror and maybe more. — mickep, Aug 30 '22 at 19:19
@mickep my own policy of course is never to make errors then these settings have no effect — David Carlisle, Aug 30 '22 at 20:37

How to get latex to ignore blank lines in equations

1 Answers1