[Tex/LaTex] Writing math formula in LaTeX, ‘undefined control sequence’

amsmathmath-modemath-operatorsmathtools

I'm using the amsmath package and writing a report. I am using a LaTeX manual pdf, which has a chapter on writing maths formulas. I have followed what it says and I do not understand why my equation is causing an 'undefined control sequence' error

I'm trying to write this maths formula:

\begin{equation}
q_k(p)= f(x_k) + \nablaf(x_k)^Tp + \frac{1}{2}p^T\nabla{^2}f(x_k)p
\end{equation}

The equation comes out nicely, except for the nabla squared term, there is some brackets around the 2 for some reason. However, the bigger problem is I can not move on because it says I have created an 'unidentified control sequence' and I do not know why.

Best Answer

You have

\nablaf

which is probably undefined, I guess you wanted

\nabla f

(Please always post a complete document that generates the error, it is much easier to debug then)

Related Solutions

[Tex/LaTex] Undefined control sequence math operators

\invneg is defined in package wasysym and package MnSymbol:

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{wasysym}
\let\wasyinvneg\invneg
\let\iint\relax
\let\iiint\relax
\usepackage{MnSymbol}
\begin{document}
\begin{tabular}{lll}
\textsf{wasysym} & \texttt{\textbackslash invneg} & $\wasyinvneg$\\
\textsf{MnSymbol} & \texttt{\textbackslash invneg} & $\invneg$\\
\textsf{MnSymbol} & \texttt{\textbackslash backneg} & $\backneg$\\
\end{tabular}
\end{document}

[Tex/LaTex] “undefined control sequence” error with curly brackets

I wouldn't use \limits in this case since it'll end up placing the lower and upper limits of the sequence below and above the right-hand curly brace -- probably not what you intended.

If you write \{h_{n}\}_{0}^{\infty}$ (see the middle example below, labelled "not awful"), the upper and lower limits may look like they're too close to each other, especially in text-style math mode. One way to fix this is to encase the closing curly brace, \}, in a pair of braces to change its status from "math-close" to "math-ordinary"; doing so will loosen the spacing quite a bit.

It may be best, though, to define a custom macro called, say, \seqwlimits to standardize the task at hand and to assure adequate vertical separation of the upper and lower limits.

enter image description here

\documentclass{article}
\newcommand\seqwlimits[3]{\{#1\}_{\mathstrut#2}^{\mathstrut#3}}
\begin{document}
\begin{tabular}{ll}
huh??    & ${\{h_{n}\}}\limits_{0}^{\infty}$\\[2ex]
awful    & $\{h_{n}\}\limits_{0}^{\infty}$\\[2ex]
not awful& $\{h_{n}\}_{0}^{\infty}$\\[2ex]
better   & $\{h_{n}{\}}_{0}^{\infty}$\\[2ex]  % note the extra { and }
best     & $\seqwlimits{h_n}{0}{\infty}$\\
\end{tabular}
\end{document}

Best Answer

Related Solutions

[Tex/LaTex] Undefined control sequence math operators

[Tex/LaTex] “undefined control sequence” error with curly brackets

Related Question