# Recreate efficiently this figure

I am writing a technical document, and I need to explain several steps of a construction which use matrices and linear equations. I was puzzled how I would create my figures and one paper I reference use this :

I have to do 6 or 7 of these, and I would like to know what is the most efficient way of doing it. In each figure the number of components and the value of equation will be different. I already know how to create individually matrices and tables. I want to know how to produce such a figure without too much sweat. I don't use latex a lot, but if you point out packages, references or any material to look at it will be a good start.

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You can use TikZ for that, but I’m not sure if this is the most efficient way, since I don’t understand how your images will differ from each other. So you only want to change some numbers in the equations?

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{shapes.misc,matrix,positioning,fit}
% some settings and style definitions
\tikzset{
boxed eqns/.style={%
matrix of math nodes,
row sep=-0.4pt,
nodes={
draw,
minimum width=1cm,
minimum height=0.6cm,
},
},
values/.style={
matrix of math nodes,
left delimiter=[,
right delimiter=],
},
equation/.style={
execute at begin node={$\displaystyle}, execute at end node={$},
},
blue box around/.style={
draw,
ultra thick,
blue,
fit=#1,
inner sep=0pt,
},
cancel/.style={
cross out,
draw,
red,
ultra thick,
fit=#1,
inner xsep=10pt,
inner ysep=1pt,
},
}

\begin{document}
\begin{tikzpicture}
\matrix (Variables) [boxed eqns] {a_1\\a_2\\a_3\\};
\matrix (Values) [values,right=of Variables] {1\\2\\3\\};
\node (Eqn) [equation,right=of Values] {a_1+a_2+a_3};
\foreach \l in {1,2,3}
\draw [->] (Variables-\l-1) -- (Eqn);
\end{tikzpicture}

\begin{tikzpicture}
\matrix (Variables) [boxed eqns] {a_1\\a_2\\a_3\\};
\matrix (Values) [values,right=of Variables] {1\\2\\3\\};
\node [blue box around=(Variables-2-1)] {};
\node [cancel=(Values)] {};
\end{tikzpicture}
\end{document}


How to get the upper picture?

1. Create the styles for different parts of your images.

• I used matrixes, that switch to math mode for their content
• I let the matrices draw the frames and delimiters
2. Set up the {tikzpicture} environment.

3. Draw the first matrix with the boxed variables.

• Us the boxed eqns style.
• Give a name to it in braces, e.g. (Variables).
• Use \\ after each variable, even the last one.
4. Draw the second matrix with the values.

• Us the values style.
• Give a name to it in braces, e.g. (Values).
• Use \\ after each value, even the last one.
• Postion it right of the first on with right=of Variables.
5. Draw the node containing the equantion.

• Us the equation style.
• Give a name to it in braces, e.g. (Eqn).
• Postion it right of the first on with right=of Values.
6. Draw the arrows

• Use \foreach to repeat the things for every item of the list {1,2,3}, and save the current item in \l.
• Set up the \draw command with -> to get an arrow tip at the end.
• Begin the path at (Variables-\l-1), which is one of the first matrix’ cell.
• End the path at (Eqn). The best end position is calculated automatically.

How to get the lower picture?

1. Draw the matrices as above.

2. Use blue box around=(<node name>) to frame a node or part of a matrix*.

3. Use cancel=(<node name>) to put a cross over a node or part of a matrix*.

* The part of a matrix is a node …

How to draw an equation system?

Add this definition to \tikzsset

eqn system/.style={
matrix of math nodes,
nodes in empty cells,
row sep=0.1cm,
column sep=0.5cm,
draw,
nodes={
anchor=base east,
},
},


and use it like this:

\begin{tikzpicture}
\matrix (ES) [eqn system] {
a_1   & + 2a_2 &        & + 4a_4 \\
10b_1 &        &        & -3b_a  \\
& -  c_2 & + 3c_3 &        \\
};
\node [blue box around=(ES-1-1) (ES-1-4)] {};
\end{tikzpicture}


But this needs some improvements as you can see in the image …

## Update

You could automat the things with a new macro

% \autodraw{<Varaibles>}{<Number of Variables>}{<Values>}{<Eqn>}
\newcommand{\autodraw}[4]{%
\begin{tikzpicture}
\matrix (Variables) [boxed eqns] {#1};
\matrix (Values) [values,right=of Variables] {#3};
\node (Eqn) [equation,right=of Values] {#4};
\foreach \l in {1,...,#2}
\draw [->] (Variables-\l-1) -- (Eqn);
\end{tikzpicture}
}


example

\autodraw{b_1\\b_2\\b_2\\}{3}{7\\2\\5\\}{2b_1+b_2-3b_3}

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Wow this is powerful! Seems like a complete language by itself, like matlab. I modified your script with : \matrix (Variables) [boxed eqns] {a_1\\a_2\\a_3\\a_4\\a_5\\a_6\\a_7\\}; \matrix (Values) [values, right=of Variables-2-1] {1\\2\\3\\}; \node (Eqn) [equation, right=of Values] {a_1+a_2+a_3}; \foreach \l in {1,2,3} \draw [->] (Variables-\l-1) -- (Eqn); –  UmNyobe Apr 13 '12 at 14:12
yes I want to modify the content of Variables, Values and Eqn. My guess will be to write a macro to put the arguments at the right position. Is there a better way?? –  UmNyobe Apr 13 '12 at 14:18
@UmNyobe: Yes TikZ is very powerful and can do even more complex things like this. It’s a user level layer of PGF which was created to do graphics. Have a look at the pgfmanual, which includes some great tutorials to learn TikZ. –  Tobi Apr 13 '12 at 14:19
@UmNyobe: I added a command to draw the things. You surely find a better name that \autodraw for it ;-) –  Tobi Apr 13 '12 at 14:25
Thanks. I will try to stand on my own feet. –  UmNyobe Apr 13 '12 at 14:39