Informatics1-2017/Practice8

A lap 2017. október 30., 07:49-kori változata

Newcommand

• With the \newcommand command we can define new commands. These should be placed in the preamble (before \begin{document})..
• We can think of it as an abbreviation.
• For example, if we write the set of real numbers a lot of times, we can do the following:

...
\newcommand{\R}{\mathbb{R}}
...
\begin{document}
\[
x^2 \geq 0 \quad \forall x\in\R
\]
\end{document}

• With this newcommand if we write \R it gets substituted with \mathbb{R}.
• The first parameter of newcommand is the name of the command (given by us), the second is the existing command (can be a set of commands) we wish to shorten.
• We could do the same for the set of integers, etc.

Arguments

• We can define complex commands, for example if we would like to make a command for a nice integral:

...
\newcommand{\myint}[2]{\int #1 \,\mathrm{d}#2}
...
\begin{document}
\[
\myint{x^2 \sin^2 x}{x} + \myint{x^2 \cos^2 x}{x} = \myint{x^2}{x}
\]
\end{document}

• Here the optional parameter [2] tells latex that the command has two arguments (inputs).
• We can specify the position of the arguments by #1, #2... Here the first parameter is the integrand, the second is the variable.

• If the command that we want to define already exists we will get an error. For example if we tried to name the previous command int instead of myint.
• If we want to forcefully redefine a command, we can use the \renewcommand that has the same syntax, but it allows to redefine existing commands.

Tasks

Sample latex document frame:

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[magyar]{babel}
 
\usepackage{amsmath}
\usepackage{amsthm}
\usepackage{amssymb}
 
\begin{document}
 
 
 
\end{document}

Halmazok

Define the set of racional and natural numbers. Try it on a simple formula.

Vector

Define a command that has one argument. All it should do is to put a right arrow over the given argument (\overrightarrow{something}). This makes it a bit easier to write vectors in formulas. Name it vec at first, and after we get an error (because the \vec command already exists), name it myvec. Try it with an arbitrary formula.

In truth this did not shorten our code all that much, since myvect is only 8 letters less. But still this is very useful when we write longer articles. Just think about a situation where we write a 20 page article using \overrightarrow to denote vectors, but then we change our mind and want to use \underline instead. Now we can use the replace all functionality (present in most text editors), but what if we used \overrightarrow somewhere else that's not a vector? It's all a mess now. Now imagine the same situation if we defined a new command for our vectors and used it throughout the document. All we have to change in this case is the definition of our vector command. This is the true value of using our own commands.