Equivalent of \ker for the image of a map

Question

I know I can use \ker in place of \text{ker} to denote the kernel of a map. Is there a similar command for the image of a map?

Even if I define my own command like

\newcommand{\Ima}{\text{Im}}

Inside the theorem environment (for example) I get the italic version of Im. How can I fix this?

I always thought this was a huge oversight; even amsmath doesn't define it. The package does seem to have a bit of a bias toward calculus, somehow. — Ryan Reich, Dec 01 '12 at 15:25
@Ryan: I think part of the issue is that Im for image is less universal than ker for kernel, perhaps because Im can also be used to denote the imaginary part of a complex number. — Charles Staats, Dec 01 '12 at 15:33
actually, \Im is already defined (in both plain tex and latex) to be a fraktur "I", so \newcommand won't work. — barbara beeton, Dec 01 '12 at 15:38
are these any help: Define additional math operators to be typeset in roman, How can I define a math operator behaving like \lim?, How do I do a one-shot MathOperator?, ... — barbara beeton, Dec 01 '12 at 15:41
@BrunoLeFloch: There's not any proper reason... I just always did it like that by hand — Abramodj, Dec 05 '12 at 07:30

score 41 · Accepted Answer · answered Dec 01 '12 at 15:14

41

You can use \DeclareMathOperator from the amsmath package to define it; in this way it will have the appropriate spacing and font:

\documentclass{article}
\usepackage{amsmath}

\DeclareMathOperator{\Ima}{Im}

\begin{document}

$\Ima f\subseteq \ker g$

\end{document}

enter image description here

answered Dec 01 '12 at 15:14

Gonzalo Medina

Thanks, that's great and it will be useful in many other cases! – Abramodj Dec 01 '12 at 15:37

1 Answers1