Math & Science ⇒ Defining terms with reference to others

[Alec W]

Hi,

I've just found Latex recently & have fallen in love with its precision. As a maths teacher I am looking to set up various general routines that I can just copy & paste into the tests that I write.

I wanted to write a general routine for making isometric dotty paper where I could simply define the size & spacing using some opening definitions & a scale command. After stumbling around for an elegant solution I ended up doing this, which works, but I wondered if anyone could advise me as to a nicer way to do it. Is it possible to define the \innerx and \innery with reference to the \outerx - 1 & \outery - 1?

This is my script

Code: Select all

\begin{tikzpicture} [scale=0.75]

\def\outery{20}
\def\outerx{10}
\def\innerx{9}
\def\innery{19}
\def\costhirty{0.8660254cm}
\def\twocosthirty{1.732050808}

	\foreach [evaluate=\a using (\twocosthirty*\b)] \b in {0,1,...,\outerx}
		\foreach \c in {0,1,...,\outery}
		\filldraw (\a,\c) circle (0.05cm) ;
	\foreach [evaluate=\d using (\twocosthirty*\e)] \e in {0,1,...,\innerx}
		\foreach \f in {0,1,...,\innery}
		\filldraw [xshift=\costhirty,yshift=0.5cm] (\d,\f) circle (0.05cm) ;
	
\end{tikzpicture}

Alec

[cgnieder]

Maybe something like this:

Code: Select all

\documentclass{article}
\usepackage{tikz}
\usepackage{etex}
% the etex package provides \loccount which enables us to
% locally define \count's

\begin{document}

\begin{tikzpicture}[scale=0.75]
  \loccount\X \loccount\Y
  \X=10 \Y=20
  \def\costhirty{0.8660254}
  \foreach [evaluate=\a using (2*\costhirty*\b)] \b in {0,1,...,\X}
    \foreach \c in {0,1,...,\Y}
      \filldraw (\a,\c) circle (0.05cm) ;
  \advance \X by -1 \advance \Y by -1
  \foreach [evaluate=\d using (2*\costhirty*\e)] \e in {0,1,...,\X}
    \foreach \f in {0,1,...,\Y}
      \filldraw [xshift=\costhirty cm,yshift=0.5cm] (\d,\f) circle (0.05cm) ;
\end{tikzpicture}

\end{document}

I use counts here which in general should only be defined only once in a document. The etex package however provides \loccount so they will stay local and could be newly defined inside other groups or environments in the same document.

If you don't like using another package and you know you will define(*) \X and \Y only once, you can replace \loccount with \newcount and leave out \usepackage{etex}.


(*) I.e., saying \newcount\X. You can use \X=<num> as many times as you like...

Regards

[Alec W]

Many thanks, that's exactly the sort of thing I was looking for.

Alec