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I'm trying to write something like: $affinity(x)$, but in the PDF I see some small spacing between the two f's.

example image

I tried $af{}firm(x)$ or $aff{}irm(x)$, but nothing works.

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In general math words should not be entered "undecorated" in TeX as they are typeset as separate letters, not as a word....which is why we use \mathit and the like. –  Yossi Farjoun Nov 27 '10 at 16:17
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3 Answers

up vote 13 down vote accepted

$\mathit{affinity}(x)$

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Thanks! that did it. –  Hagai Cibulski Nov 27 '10 at 14:03
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$affinity$ stands for the product of the variables a, f, f, i, …. Wordlike functions are usually written in an upright font, usually with \DeclareMathOperator:

\usepackage{amsopn}
\DeclareMathOperator{\affinity}{affinity}
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I agree, just wrote it at the same time :) just with an example. –  Stefan Kottwitz Nov 27 '10 at 16:44
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How do you usually write maps, functions and operators in your math text? Italic as well?

Math operators are commonly written in upright letters, in contrary to variables which have italic shape. I would use \mathrm instead of \mathit or better

\DeclareMathOperator{\affinity}{affinity}

of amsmath, and write \affinity in the formulas. Here's a complete example, just compare:

\documentclass{article}
\usepackage{amsmath}
\DeclareMathOperator{\affinity}{affinity}
\begin{document}
\[
  \affinity(x) \neq \mathit{affinity}(x) \neq y(x),
\]
\[
  \max_f \lim_a af = a\cdot f
\]
\end{document}

Output:

alt text

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