! Missing Inserted for Ifnumto Be Read Againl283 ?

Contents

• 1 How to fix this mistake
  • ane.ane The primary causes of Missing $ inserted
  • ane.2 Examples of errors and their solutions
    • 1.2.one Symbol commands must be used in math mode
      • 1.two.one.1 Fixing errors caused by LaTeX symbol commands
      • one.ii.1.2 A list of LaTeX symbols
    • 1.two.2 Using math-mode-only characters outside math mode
      • 1.2.2.1 Using underscores outside of math mode
      • 1.2.2.2 Using underscores in URLs
      • 1.2.2.three Underscores in .bib file URLs
    • 1.2.3 Using commands non permitted in math mode
    • ane.2.4 Blank lines in mathematics
    • 1.2.5 Using $ within math environments
• ii Background to the Missing $ inserted error
  • 2.1 In that location are no missing $ signs but I still become the fault
  • ii.ii Of modes, and when
    • 2.two.1 Math manner
    • two.2.two Triggering TeX math modes
    • 2.2.iii Macros: testing for math fashion
• 3 Advanced: An explanation of TeX's mistake recovery mechanism
  • iii.1 Worked instance

How to fix this mistake

This fault tin be triggered in dissimilar ways and, especially for those new to LaTeX, it's not e'er immediately obvious why it happened, or, more importantly, how to resolve information technology. We'll start with an overview of the full general conditions which trigger this error then list some of the more common causes and how to prepare them. The latter parts of this article offering more than in-depth material for readers wishing to broaden their agreement.

Note: In this article we use the terms "TeX", "LaTeX" and "TeX engine" but if yous aren't sure of their different meanings you can find out in the Overleaf article What'southward in a Name: A Guide to the Many Flavours of TeX.

The main causes of Missing $ inserted

In that location are three master reasons why (La)TeX generates this mistake:

1. You've fabricated an explicit fault in your math markup, such as writing $y=f(x)$$—we look at other examples after in this article.
2. TeX has detected a character or command designed to be used merely when TeX is typesetting mathematics but that character or command has been used when TeX was not typesetting mathematics.
   • TeXnically speaking: TeX detected a character or command designed to work inside math style but you've tried to apply information technology outside math mode. To clarify the consequence with "characters" designed to work in math mode, what we really mean is using characters assigned sure category codes designed to operate within mathematical cloth.
3. TeX has detected a command designed to be used only when TeX is not typesetting mathematics but that control was detected (used) whilst TeX was typesetting mathematical material.
   • TeXnically speaking: TeX detected a control designed to piece of work outside math mode merely you've tried to utilise information technology inside math mode.

Examples of errors and their solutions

The following examples demonstrate some means in which the Missing $ inserted mistake can exist triggered, together with providing solutions to resolve the error.

Symbol commands must exist used in math mode

Many math symbols in LaTeX are accessed using commands which must simply be used when TeX is typesetting math; i.eastward., at a time when TeX is in math mode.

Examples of commonly-used symbol commands include those for Greek letters: \alpha \((\alpha)\), \beta \((\beta)\), \gamma (\(\gamma)\), \delta \((\delta)\), \Delta \((\Delta)\) and and so forth. Many other LaTeX commands, such equally those for modifiers: \vec{x} \((\vec{x})\), \tilde{x} \((\tilde{x})\), \hat{x} \((\chapeau{x})\) etc., are as well designed for use in math mode.

Using modifiers, symbol commands—and many other math-related commands—outside of typesetting mathematical content volition generate a Missing $ inserted error and forcefulness the compiler to enter into math mode.

The following example shows what happens if you try to use the command \alpha \((\blastoff)\) exterior of math (style):

            Writing            \verb|\alpha| outside math mode will generate an error:            \alpha            and then this text will not be typeset correctly...          

 Open up this error-producing example in Overleaf

The post-obit prototype shows function of the output produced past the LaTeX lawmaking above, demonstrating the fault caused past using \blastoff exterior of math mode:

Fixing errors caused by LaTeX symbol commands

To use modifiers, or Greek math symbols, inside sentences they must always be wrapped in single dollar signs $...$, or LaTeX'southward \(...\) syntax, in guild for TeX to process them in inline math mode, equally shown beneath.

            When writing the Greek letter blastoff in a sentence, it must be written as            \verb|$            \alpha            $| to generate            $            \alpha            $,  or as            \verb|\(            \alpha            \)| which also generates            \(            \alpha            \).   When writing a vector x in a sentence, it must be written as            \verb|$            \vec            {10}            $| to produce            $            \vec            {x}            $            or as            \verb|\(            \vec            {x}            \)| which also yields            \(            \vec            {x}            \).          

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A list of LaTeX symbols

The Overleaf commodity List of Greek letters and math symbols provides a list of symbols which are exclusive to math mode, together with links to further useful resources.

Using math-mode-simply characters exterior math mode

Traditionally, TeX/LaTeX reserve certain common characters for apply within math mode:

• ^: reserved for creating superscripts
• _: reserved for creating subscripts
• $: reserved for starting/stopping math mode

Using them straight outside math manner triggers errors.

• To type $ outside math manner use \$
• To type _ exterior math fashion apply \_
• Multiple means to blazon ^ exterior math mode. A listing is provided on tex.stackexchange

Using underscores outside of math mode

A common cause of the Missing $ inserted fault is using underscores (_), a math mode character, outside of math style—such as underscores present in filenames: an example of this is shown below.

            Using a math character, such as an underscore, in a file proper noun: math_case.tex.          

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Considering the underscore grapheme is assigned category lawmaking 8 information technology is reserved for creating subscripts when the TeX engine is in math mode. Consequently, when (La)TeX detects the _ in the file name math_example.tex it does so outside of math way, which triggers an error and results in erroneous typesetting of subsequent text:

\(\text{Using a math character, such every bit an underscore, in a file proper noun: math}_example.tex.\)

The _ grapheme (technically its category code of 8) triggers an mistake and causes TeX to enter math manner: the alphabetic character eastward following immediately after the _ is treated as a character to be typeset as a subscript. Processing then continues in math mode resulting in the italicized text and, additionally, there is no style here for TeX to gracefully go out math mode, which will trigger farther errors.

In order to avert this particular error, yous must e'er use _ in math manner—i.e., inside $..$, $$...$$ or, preferably, within LaTeX'southward notation of \(...\) and \[...\].

Outside math mode you lot need to write \_ to employ or typeset an underscore, as shown in the corrected version of the example:

            To apply the math-mode underscore character in a file name, write it like this: math\_case.tex.          

 Open this corrected version on Overleaf

Using underscores in URLs

Yous may also come across this error when trying to typeset URLs with underscores, east.thousand. https://www.overleaf.com/learn/latex/Subscripts_and_superscripts. Instead of escaping each underscore character, you lot may want to load the url or hyperref packet, and then apply the \url command like this:

                        \documentclass            {article}            \usepackage            {url}            \begin            {document}            \url            {https://www.overleaf.com/learn/latex/Subscripts_and_superscripts}            \cease            {certificate}          

 Open this example in Overleaf

Underscores in .bib file URLs

If such URLs are in your bibliography .bib file, causing errors to be reported from the .bbl file, and then make certain y'all utilize the url or doi fields to tape these fields in the .bib file:

doi = {10.1007/978-94-015-6859-3_4}, url = {https://abc.com/latest_news_1.html}

and load the url or hyperref package in your preamble, if necessary. Most bibliography style files will then be able to automatically wrap these values in a \url{...} command.

Using commands non permitted in math fashion

A number of low-level built-in TeX commands (called primitives) are not permitted in math mode and their apply in math style volition trigger the Missing $ inserted error. Although most users are unlikely to utilise these commands in day-to-twenty-four hours LaTeX lawmaking, we make a note here because it's possible they could be contained inside LaTeX commands (macros) being used in math way.

The following case tries to use the TeX control \vskip inside mathematical material. This is not permitted and generates an error.

                        \documentclass            {article}            \begin            {document}            I want to add some infinite, but this is non the mode to do it...            \[            y            =            f            (            x            )                                    \vskip            five            pt z            =            f            (            y            )            \]            $            y            =            f            (            x            )                                    \vskip            5            pt z            =            f            (            y            )            $            \end            {certificate}          

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Other TeX (archaic) commands not permitted when TeX is in math way include \par, \hrule, \unvbox, \unvcopy and \valign.

Bare lines in mathematics

                        \documentclass            {commodity}            \brainstorm            {document}            \begin            {equation}            y=x^3,  z=x^3            \cease            {equation}            \terminate            {document}          

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Cause: The blank line between the formulae is converted to a \par command which is not allowed in math mode. You can too see this by writing

                        \documentclass            {article}            \brainstorm            {document}            \[            y            =            x^            3            ,            \par                          z            =            ten^            three            \]            \stop            {certificate}          

 Open this fault-generating lawmaking on Overleaf

To gear up this, either delete the blank lines or annotate them out:

                        \documentclass            {article}            \brainstorm            {certificate}            \begin            {equation}            y=10^3,            % This will suppress the blank line            z=x^3            \end            {equation}            \end            {document}          

 Open this corrected version on Overleaf

Using $ inside math environments

Some LaTeX environments, such as the align and equation environments, do non require math to be wrapped in $ signs, or use of LaTeX's math syntax: \(...\) or \[...\]. The LaTeX code which implements those environments takes intendance of entering and exiting math style.

The following case shows use of the $ sign inside an amsmath marshal surroundings, which triggers a Missing $ inserted error, among many others....

                        \documentclass            {article}            \usepackage            {amsmath}            \begin            {document}            \begin            {marshal*}            $            2            x                        -                                    5            y &            =                                    8                                    \\                                    three            10                        +                                    9            y &            =                                    -            12            $            \finish            {align*}            \end            {document}          

 Open this error-generating code on Overleaf

The right way to write these equations is:

                        \documentclass            {commodity}            \usepackage            {amsmath}            \brainstorm            {document}            \begin            {align*}            2x - 5y            &=  8            \\            3x + 9y            &=  -12            \finish            {align*}            \cease            {document}          

 Open this corrected version on Overleaf

Groundwork to the Missing $ inserted fault

The following section is for readers wishing to amend understand the reasons backside the error Missing $ inserted. It'due south not essential reading merely it may assist you lot with finding and fixing errors.

There are no missing $ signs but I still get the error

In some circumstances the Missing $ inserted fault can be very confusing because your LaTeX code might not really have any problems with visibly missing $ characters. For example, the LaTeX fragment \(\verb|$$y=f(x)\par$$|\) superficially looks correct: the \(\verb|$$|\) pairs are balanced just it will trigger the "missing $" error. Here, it is due to the \par control which is not allowed in math manner:

                        \documentclass            {commodity}            \begin            {document}            This instance generates the mistake            \verb|Missing            $                          inserted|:                        $$            y            =            f            (            10            )            \par            $$                        \end            {document}          

 Open this to see a Missing $ inserted fault

The above LaTeX code actually triggers a cascade of errors, equally shown below, so clearly you should non use \par inside math!

! Missing $ inserted. <inserted text>                  $ fifty.12 $$y=f(ten)\par                  $$ I've inserted a begin-math/end-math symbol since I remember yous left one out. Continue, with fingers crossed.  ! Display math should finish with $$. <to be read again>                     \par  l.12 $$y=f(x)\par                  $$ The `$' that I just saw supposedly matches a previous `$$'. So I shall assume that you typed `$$' both times.  ! Missing $ inserted. <inserted text>                  $ l.thirteen \end{document}                     I've inserted a begin-math/terminate-math symbol since I think you left one out. Proceed, with fingers crossed.  ! Display math should stop with $$. <to be read again>                     \par  l.13 \cease{document}                     The `$' that I simply saw supposedly matches a previous `$$'. So I shall assume that you typed `$$' both times.          

When the Missing $ inserted mistake occurs the TeX engine software is trying to recover and "get back on runway" and then it tin go on processing afterward the signal where the error occurred. The section Advanced: An explanation of TeX'southward error recovery mechanism will help you sympathise why this pour of errors arises due to TeX's attempts at trying to fix the initial error.

Of modes, and when

Internally, TeX engines are designed operate using three "states of listen", called modes, which depend on the type of material a TeX engine is currently typesetting. The way a TeX engine is in at any point during typesetting is called its current fashion, which changes throughout the process of typesetting the content of your LaTeX document.

For each of a TeX engine's modes there are certain commands and characters (or, more than correctly, category codes) which are "incompatible" with TeX'due south current mode: they shouldn't exist used whilst TeX is in that specific mode. If you try to use those inappropriate characters or commands TeX volition issue an error such equally Missing $ inserted to tell you something is wrong.

Math mode

This error Missing $ inserted is related to TeX's math mode—i.e., the mode a TeX engine is in when yous ask LaTeX to typeset some maths.

Simply for completeness nosotros'll note there are two types of math mode, reflecting the cosmos of inline or display math:

• inline math mode
• display math mode

TeX needs these 2 different math modes because it applies unlike rules for spacing, symbols sizes etc when typesetting math destined for inline or brandish.

Triggering TeX math modes

There are multiple means to trigger a TeX engine to enter and then get out math mode.

• You can use explicit markup such every bit:
  • LaTeX syntax: \(...\) to enter \( then leave \) inline math mode or \[...\] to enter \[ then exit \] display math mode;
  • (historic) TeX syntax: $...$ to enter (first $) then get out (second $) inline math mode or $$...$$ to enter (offset $$ pair) then go out (second $$ pair) brandish math mode;
• or any ane of the LaTeX math environments:
  • \begin{align}...\stop{align} etc. Backside the scenes these surroundings take care of entering and leaving math manner.

The actual text of the bulletin Missing $ inserted is built into ("hardcoded" in) TeX engine software, which is why you will notwithstanding meet Missing $ even if you are non using $ characters to typeset mathematics and use purely LaTeX syntax to markup the math in your document. This can be confusing to new users of LaTeX just in that location's fiddling that can exist done to change this error message text without modifying the source lawmaking of TeX engines!

Macros: testing for math mode

It'due south possible to test if TeX is currently in math mode using the primitive command \ifmmode; that manner you tin can write macros whose behavior can adapt to avoid generating manner-related errors. Here is a very basic example to demonstrate the principle, which prints Yep. or No. depending whether or not TeX is in math mode at the point of "executing" the macro.

                        \documentclass            {commodity}            \begin            {document}            \newcommand            {            \mytest            }{            \ifmmode            \mathrm            {Yes}            \else            No\fi.}            Is the macro being used in math mode?            $            \mytest            $            Is the macro being used in math fashion?            $$            \mytest            $$            Is the macro being used in math mode?            \(            \mytest            \)            Is the macro beingness used in math mode?            \[            \mytest            \]            Is the macro beingness used in math fashion?            \mytest            \end            {document}          

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The following graphic shows the output produced by the example above:

Advanced: An explanation of TeX's error recovery mechanism

The error message Missing $ inserted is not output by Overleaf, LaTeX, or LaTeX packages; it actually originates from within the executable plan responsible for typesetting your LaTeX document: that executable program is called a TeX engine—yous tin think of it as "driving" the typesetting process.

Within the source code of the TeX software, its author (Donald Knuth), makes this observation about the lawmaking responsible for generating the Missing $ inserted error:

Here is a list of cases where the user has probably gotten into or out of math way past error. TeX will insert a dollar sign and rescan the electric current token.

At the centre of the Missing $ inserted fault is TeX detecting "something" that should not take been used inside math mode, or "something" expressly designed for math typesetting existence used outside math mode.

The task facing TeX is: How do I recover from this? TeX does exactly what Knuth writes: it inserts a dollar sign and rescans the electric current token—a "token" is TeX's internal numeric (integer) value which represents the character or command it has just read in. However, due to the precise context of the error, this strategy may, or may non, be successful—as the error text goes on to say "Proceed, with fingers crossed."!

Worked example

Let's explore Knuth's comments past taking a closer look at the following case: \(\verb|$y=f(x)$$\vskip3pt|\). If you open the code below you'll see information technology triggers the error Missing $ inserted.

            Writing            \verb|$            y            =            f            (            ten            )            $$            \vskip            3            pt| produces...            $y=f(10)$$            \vskip            3            pt Showtime new line...          

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To review why this triggers an error permit's write subscripts to identify each \(\verb|$|\) in the expression to obtain \(\verb|$|_{\mathtt1}\verb|y=f(ten)|\verb|$|_{\mathtt2}\verb|$|_{\mathtt3}\verb|\vskip3pt|\). TeX is able to correctly process the commencement function \(\verb|$|_{\mathtt1}\verb|y=f(x)|\verb|$|_{\mathtt2}\) which is treated as a correctly formatted piece of inline math, producing \(y=f(x)\). Immediately after processing \(\verb|$|_{\mathtt2}\) TeX temporarily exits inline math mode—in our example we are creating inline math in a paragraph so it briefly enters then-chosen horizontal style.

It'southward what happens next that triggers the mistake. TeX continues to process the \(\verb|$|_{\mathtt3}\) which triggers TeX to re-enter inline math mode. TeX now reads the side by side token which is the \(\verb|\vskip|\) command—it has non yet read the \(\verb|3pt|\). At this point, TeX sees \(\verb|\vskip|\) merely information technology'due south in inline math mode: \(\verb|\vskip|\) is not allowed there so information technology triggers TeX's error-handling process as described by Knuth:

TeX volition insert a dollar sign and rescan the current token.

Here, the current token is the \(\verb|\vskip|\) command and so what TeX does is place a new $ into its input, let's call it \(\verb|$|_{\mathtt4}\). At this point, TeX is still in inline math mode just now it goes dorsum to read the equivalent of \(\verb|$|_{\mathtt4}\verb|\vskip|\) which is read in inline math way. The \(\verb|$|_{\mathtt4}\), inserted past TeX itself, at present closes the current inline math mode and TeX goes on to read the \(\verb|\vskip|\) command outside inline math style—here, TeX is in a paragraph so the \(\verb|\vskip3pt|\) causes the current paragraph to be ended and \(\verb|3pt|\) of space placed after it.

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Source: https://www.overleaf.com/learn/latex/Errors/Missing_$_inserted

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