[Tex/LaTex] error-how to solve the Undefined control sequence

equations

Undefined control sequence.
l.226 ... 1}} = \mathop {\arg \min }\limits_X {\rm
                                                  { }}L(X,{Y_k},{Z_k},\beta )\\

How to solve issue?
which is from:

\begin{equation}
\begin{array}{l}
{X_{k + 1}} = \mathop {\arg \min }\limits_X {\rm{ }}L(X,{Y_k},{Z_k},\beta 
)\\
{\rm{       }} = \mathop {\arg \min }\limits_X {\rm{ }}{\left\| X 
\right\|_*} + {\raise0.7ex\hbox{$\beta $} \!\mathord{\left/
{\vphantom {\beta  2}}\right.\kern-\nulldelimiterspace}
\!\lower0.7ex\hbox{$2$}}\left\| {X - (Y_k - {\raise0.7ex\hbox{$1$} 
\!\mathord{\left/
{\vphantom {1 \beta }}\right.\kern-\nulldelimiterspace}
\!\lower0.7ex\hbox{$\beta $}}Z_k)} \right\|_F^2
\end{array}
\end{equation}

Can anyone help me solve this error?

Best Answer

You have reformatted the error message which obscures which command is undefined.

Also you did not provide a test file.

If you set your example using article it works without error

\documentclass{article}

\begin{document}

\begin{equation}
\begin{array}{l}
{X_{k + 1}} = \mathop {\arg \min }\limits_X {\rm{ }}L(X,{Y_k},{Z_k},\beta 
)\\
{\rm{       }} = \mathop {\arg \min }\limits_X {\rm{ }}{\left\| X 
\right\|_*} + {\raise0.7ex\hbox{$\beta $} \!\mathord{\left/
{\vphantom {\beta  2}}\right.\kern-\nulldelimiterspace}
\!\lower0.7ex\hbox{$2$}}\left\| {X - (Y_k - {\raise0.7ex\hbox{$1$} 
\!\mathord{\left/
{\vphantom {1 \beta }}\right.\kern-\nulldelimiterspace}
\!\lower0.7ex\hbox{$\beta $}}Z_k)} \right\|_F^2
\end{array}
\end{equation}
\end{document}

\documentclass{scrartcl}

koma script defines \rm to give an error:

! Class scrartcl Error: undefined old font command `\rm'.

See the scrartcl class documentation for explanation.
Type  H <return>  for immediate help.
 ...                                              

l.7 ... + 1}} = \mathop {\arg \min }\limits_X {\rm
                                                  { }}L(X,{Y_k},{Z_k},\beta
?

other classes may not define \rm at all in which case you get the primitive undefined command error message but again with a line break highlighting the issue

\documentclass{minimal}

! Undefined control sequence.
l.7 ... + 1}} = \mathop {\arg \min }\limits_X {\rm
                                                  { }}L(X,{Y_k},{Z_k},\beta
?

Normally use of \rm should be replaced by \mathrm but here it is applied to nothing so it is simpler just to delete it \{\rm{ }} is the same as {}.

A more reasonable markup might be

\documentclass{article}

\usepackage{amsmath,nicefrac}
\begin{document}

\begin{equation}
\begin{aligned}
X_{k + 1} &= \mathop {\arg \min }_X L(X,{Y_k},{Z_k},\beta)\\
& = \mathop {\arg \min }_X \| X\|_* + \nicefrac{\beta}{2}
\| X - (Y_k - \nicefrac{1}{\beta}Z_k)\|_F^2
\end{aligned}
\end{equation}
\end{document}

Related Solutions

[Tex/LaTex] Undefined Control Sequence,Missing $ and Display math should end with $$

use

\begin{equation}\label{eqn: current}
I_{FS} = \sum_{\substack{i}}*\frac{1}{2}*\frac{W}{L}*(V_{gs}-V_{th})^2*(1+\lambdaV_{ds})=\frac{1}{2}*k*(V_{gs}-V_{th})^2*(1+\lambda*V_{ds})*\sum_{\substack{i}}*\frac{W}{L}
\end{equation}

without the $ ...$ They are only for inline math mode, see http://mirror.ctan.org/info/math/voss/mathmode/Mathmode.pdf

[Tex/LaTex] List of equations, including equation contents and caption

Since you want a cheat sheet, I'd recommend the extract package. With a slightly different MWE:

\documentclass{article}
\usepackage[
  active,
  header=false,
  copydocumentclass=true,
  generate=\jobname-Cheatsheet,
  extract-env={equation},
  extract-cmdline={synopsis},
  ]{extract} % http://ctan.org/pkg/extract
\begin{extract*}
% Items executed in both the main and extracted document
% (extract manual, section 5.1)
\usepackage{amsmath}
\end{extract*}
\begin{extract}
% Items executed only in extracted document
\def\synopsis#1{#1}
\end{extract}
\def\synopsis#1{}
\begin{document}
First Euler observed that
\synopsis{Euler's equation tying together the five fundamental constants of mathematics}%
\begin{equation}
1 + e^{i \Pi} = 0.
\end{equation}

Then, Gauss discovered the normal distribution:
\synopsis{Normal distribution}%
\begin{equation}
P(x) = \frac{1}{{\sigma \sqrt {2\pi } }}e^{{{ - \left( {x - \mu } \right)^2 } \mathord{\left/ {\vphantom {{ - \left( {x - \mu } \right)^2 } {2\sigma ^2 }}} \right. \kern-\nulldelimiterspace} {2\sigma ^2 }}}
\end{equation}

Finally, Einstein proclaimed: 
\synopsis{Equivalence of mass and energy}%
\begin{equation}
E = m C^2
\end{equation}
\end{document}

you get an original document of:

enter image description here

and an extracted document of:

\documentclass{article}
% Items executed in both the main and extracted document
% (extract manual, section 5.1)
\usepackage{amsmath}
% Items executed only in extracted document
\def\synopsis#1{#1}

\begin{document}

\synopsis{Euler's equation tying together the five fundamental constants of mathematics}%

\begin{equation}
1 + e^{i \Pi} = 0.
\end{equation}

\synopsis{Normal distribution}%

\begin{equation}
P(x) = \frac{1}{{\sigma \sqrt {2\pi } }}e^{{{ - \left( {x - \mu } \right)^2 } \mathord{\left/ {\vphantom {{ - \left( {x - \mu } \right)^2 } {2\sigma ^2 }}} \right. \kern-\nulldelimiterspace} {2\sigma ^2 }}}
\end{equation}

\synopsis{Equivalence of mass and energy}%

\begin{equation}
E = m C^2
\end{equation}

\end{document}

and:

enter image description here

This also works with your original \caption command.

Best Answer

Related Solutions

[Tex/LaTex] Undefined Control Sequence,Missing $ and Display math should end with $$

[Tex/LaTex] List of equations, including equation contents and caption

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