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

If I want to use the function sin in LaTeX, I write $\sin x$ or $\sin(x+1)$. If I want to use the function arctanh, I can't use $\arctanh x$:

! Undefined control sequence.
<argument> ...\ (\cos x)' &= -\sin x \\ (\arctanh 
                                                  x)' &= \frac {1}{\sqrt {1 ...
l.74 \end{align*}

? 
! Emergency stop.

What should I use instead for arctanh?

I thought of $\text{arctanh} x$, but this doesn't leave a space after arctanh. Additionally, it seems to be semantically incorrect, as arctanh is not "only" text.

marked as duplicate by egreg, Torbjørn T., user9467, Marco Daniel, clemens Sep 16 '12 at 10:17

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  • You could also use \atanh{x} of the physymb package. It gives tanh^-1. – Harold Cavendish Sep 16 '12 at 9:55
  • 3
    arctanh is semantically wrong. The right word is artanh, where "ar" is the abbreviation for area and not for arc. – Luigi Sep 16 '12 at 11:25
16

\text is not well suited for this, use

\usepackage{amsmath}
\DeclareMathOperator\arctanh{arctanh}

then \arctanh behaves like \tan and friends

  • 3
    typo: MathOperator not MahOperator – David Carlisle Sep 16 '12 at 10:06

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