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Very often I have to write \text{im}(f), to denote the image of f, if I try to write, \im f, then it generates the Imaginary notation which I do not want, if I write im f then it looks awful. Is there a way to tell my editor to recognize \im to generate \text{im} so that I do not need to write it every time?

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  • Please do not ever use \text to mark a mathematical construction! It is for textual comments only! This is a very common mistake. Why so bad? \textit{$\text{im}(f)$} gives an italic im which is not correct. Ians solution is the proper one.
    – daleif
    Jun 12, 2015 at 7:05
  • @daleif In all my time using Latex, I never had a problem that you describe. Perhaps, I am lucky, but it could just be a theoretical problem? Jun 12, 2015 at 8:33
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    You have just been lucky. Considering that most people use italics for their theorem statements, thus \text switch to italics inside theorems and definitions). \text{Im} does not get the proper spacing either (Ians solution does). I see this error a lot among students. The two most common mistakes is (1) the one you do here, and (2) X_{\text{max}} which suffer from the same problem. Here \mathrm or even \textup is more correct.
    – daleif
    Jun 12, 2015 at 9:14

2 Answers 2

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Why not create a new macro? You could do

\usepackage{amsmath}

and then

\DeclareMathOperator\Img{Im}

after which \Img creates the notation that you want, with correct spacing.

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You can use

\newcommand{\im}{\operatorname{Im}}

or go with amsmath and use @Ian_Thompson's solution, which is my favorite. These two solutions give a proper mathematical spacing but select a font automatically.

If math spacing is not required, use

\newcommand{\im}{\mathrm{Im}}

To get math spacing with font selection use

\newcommand{\im}{\mathop{\mathrm{im}}}

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