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I am using imakeidx to make multiple indices for my report, but I ran into a problem where I get an "Undefined Control Sequence" error when I try to compile. The problem is shown below.
When I open the specified .ind file, I see this.
Considering I've never had to worry about .ind files before, I did not modify this file. The code that produces that index entry is here.
I'm not quite sure what is wrong with this declaration, since I've never had problems with imakeidx before.
the problem here is the presence of a | in a string that is being written into
an \index entry.
the | has a special function in index entries: it substitutes for (and is
interpreted as) a backslash for commands that are relevant to the indexing
process, such as \see (input as |see in \index{...}) or the "brackets"
that indicate a page span, |( and |).
the proper way to input this character in an index entry depends on whether it is in math or text.
in text, a | can be "quoted" by preceding it with a ditto mark: "|.
in math, the proper substitution is \vert, or, if the
string to appear in the index output is ||, then \Vert. since these are
often paired, \lvert ... \rvert or \abs{...} (or the equivalents for the
double forms) are often more appropriate.
.idx file that is failing? and what does it become in the .ind file?
Oct 20, 2016 at 21:30
Barbara Beeton pointed out (https://tex.stackexchange.com/a/326635/220244) that | has a special function in index entries, which causes the problem.
This problem occurs, for example, if
\index(maintopic!subtopic)
was accidentally misspelled to
\index(maintopic|subtopic)
\ATwhich I never heard about.\ ATie a control-space followed by AT, that one you have\ATwhich is an undefined commandimakeidxpackage we should blame @egreg.\indexitem in the LaTeX, I specify\index{P00-F120DG-AA | AT-101-042}, so I'm not sure how that turns into\item P00-F120DG-AA , \hyperindexformat{\AT-101-042}{29}. In fact, looking at a test file I made, the IND line should be:\item P00-F120DG, \ AT-101-042{29}. I'm confused whyimakeidxis formatting is strangely.|symbol has a special meaning in any*makeidxcontext -- it is the substitute for a backslash to control commands like\see. instead of a literal|, substitute\vert\(there is a space at the end). and it might be helpful to check some documentation formakeidxorimakeidx. there is an example of the use of|in the latter documentation, in section 5.2.5:{...{#1|innote}}. (there are probably better references, but i haven't time to look just now.)