# How to type error function in LaTeX math environment [duplicate]

Possible Duplicate:
Define additional math operators to be typeset in roman

It may be a very simple question to people who know.

If I want to type commonly used functions like exponential function exp(x) or sinusoidal function sin(x), I use \exp(x) and \sin(x) in LaTeX and the results looks nice (fonts become different from other non-function characters). However, when I type error function \erf(x), it gives me error messages. If I remove \, it compiles fine but the "erf(x)" fonts just look the same to other non-function characters. Could anyone please tell me how to make the error function fonts look like as exponential function in a math environment? Thanks very much.

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## marked as duplicate by Loop Space, tohecz, Seamus, barbara beeton, WernerAug 17 '12 at 15:10

\DeclareMathOperator\erf{erf}

not every command imaginable are defined by default (assumes amsmath of course)