# Undefined control sequence in align

\begin{align}
\label{eq:x}
x = \sign{a} \cdotp \sign{b} \cdotp \min(\lvert a \rvert,\lvert b \rvert)
\end{align}


Above gives me Undefined control sequence. Any ideas would be helpful.

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Can you turn your snippet into a complete MWE? It'll help both you and anyone that might be able to help :) –  cmhughes Aug 26 '12 at 20:05
@mishr: Yes, the "master" file could have a bunch of definitions that can be used by other parts. As long as it is loaded before the others. –  Werner Aug 26 '12 at 20:13
Thanks for the information @Werner –  mishr Aug 28 '12 at 16:13

Taking a hint from egreg, add

\newcommand*{\sign}{\mathop{\mathrm{sign}}\nolimits}


to your document preamble which would provide a sign operator. However, since you're loading amsmath,

\DeclareMathOperator{\sign}{sign}


would be more robust.

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