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I am used to define some complicated and frequent mathematical expressions to be able to use them easily in my papers. For example I have defined \def\c{{\mathbb{C}}} for $\mathbb{C}$ (the field of complex numbers).

However sometimes there are more complicated formulas and mathematical expressions which involve one, two, or more variables (or parameters). For example, consider $Hom_{\mathbb{Z}} (M,N)$ which involves two variables $M$ and $N$.

My question is "how can I define such expressions generally with the ability to change the variable inside them.

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Are you looking for a way to define macros with parameters? For example \Homz{M}{N} to give this output? – marczellm Jan 24 '13 at 12:08
Yes something like that. How is it possible? – Vahid Shirbisheh Jan 24 '13 at 12:11
A suggestion: don't use \c for some command (for example, complex numbers). I'm warning because it happened to me. I got a file with this personal command used a lot of times and I was not able to use the \c c to produce ç. So some find/replace was necessary. – Sigur Jan 24 '13 at 12:11
up vote 8 down vote accepted

These are not variables in "typesetting sense". You could define


and then use


for getting

HomZ(M, N)

but this is no way more expressive or readable than


after having defined


Actually, I contend that the latter form is much more readable than the first one.

Note. Be careful in saying


because \c is an "accent command" in LaTeX (\c{c} is used in French, Albanian, Turkish, Portuguese, Catalan and other languages). Always use \newcommand or, if you really know what you're doing, \renewcommand; but don't redefine general use commands: if one of your bibliography items contains a "ç" you'll regret having redefined \c.

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I had that problem with ç. See my comment above... lol – Sigur Jan 24 '13 at 12:15
@egreg: Thank you. It is exactly what I was looking for. It may seem less readable, but it will help me in writing papers. – Vahid Shirbisheh Jan 24 '13 at 12:23
@VahidShirbisheh I don't think so. I tell you because I used that way in my first experiences with TeX/LaTeX and changed my mind after seeing that it doesn't shorten the typing nor it makes the input more readable. – egreg Jan 24 '13 at 12:46

On the preamble, use


to define math operators. For example, you can use


to define the command \Hom, and use it as $\Hom_Z(M,N)$. Compare with $Hom_Z(M,N)$.

enter image description here

Now, if you want to insert the modules as variables, you can define a new command and pass them like you do with \frac{}{}, for example.


So you can format any variable globally just formating the #1, for example.

share|improve this answer
Could you give an example how it works? How should I introduce the variables? – Vahid Shirbisheh Jan 24 '13 at 12:03
Thanks Sigur. But it does not look that much easier. I am looking for a way to define the whole bifunctor Hom with the ability to use different modules M and N whenever I needed. – Vahid Shirbisheh Jan 24 '13 at 12:10
But it is the same: type \Hom(M,N) with () or \Hom{}{} with {} 2 times takes almost the same time. I believe that the right way is to use it as operator, to format the font shape. But arguments to it, I think irrelevant. – Sigur Jan 24 '13 at 12:14
I just tried \newcommand{\Hom}[3]{\operatorname{Hom}_{\mathbb{#1}}(#2,#3)} and it works perfectly. I am sure it will help me to save time in writing repeated formulas with different variables. – Vahid Shirbisheh Jan 24 '13 at 12:26

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