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x = \sign{a} \cdotp \sign{b} \cdotp \min(\lvert a \rvert,\lvert b \rvert)

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
Yes, forgot to add newcommand in this file. Thanks @Werner . This raises another question, can newcommand be added to master file and used in file which are included from master file ? – shrm Aug 26 '12 at 20:10
@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 – shrm Aug 28 '12 at 16:13
up vote 6 down vote accepted

Taking a hint from egreg, add


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


would be more robust.

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