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Could some one help me to draw the following picture with Latex ( using only 1 picture) ? Thank you SO MUCH for your help.

enter image description here

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    Welcome to TeX.SX. Questions about how to draw specific graphics that just post an image of the desired result are really not reasonable questions to ask on the site. Please post a minimal compilable document showing that you've tried to produce the image and then people will be happy to help you with any specific problems you may have. See minimal working example (MWE) for what needs to go into such a document.
    – erik
    Commented Apr 28, 2015 at 20:52
  • Dear Erik, I am pretty new with Latex and to bo honest I don't know where to start beside searching on Google but I cannot not find an answer on it.
    – duy nguyen
    Commented Apr 28, 2015 at 21:18
  • What you need is called TikZ. Your simple drawing is covered in the tutorial of the manual: texample.net/media/pgf/builds/pgfmanualCVS2012-11-04.pdf Commented Apr 28, 2015 at 21:24
  • Although the tikz manual makes 800 pages, you should get to the point easily by looking at chapter 19. Trees are commons in tikz, see for instance texample.net/tikz/examples/feature/trees .
    – Clément
    Commented Apr 28, 2015 at 21:27

1 Answer 1

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Here's an example of how to get started. I think it should make it clear enough how to continue to get the diagram you want.

\documentclass[border=10pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{calc}
\begin{document}

\begin{tikzpicture}[my midway label/.style={midway,yshift=1.5in}]

  %% case 1
  \node[anchor=east] (A/left)         at (0,0)                  {$x$};
  \node[anchor=west] (A/right)        at ($(A/left)+(1in,0)$)   {$x$};
  \node[anchor=west] (A/right/up/1)   at ($(A/right)+(0,1in)$)  {$x+dx$};
  \node[anchor=west] (A/right/down/1) at ($(A/right)+(0,-1in)$) {$x-dx$};

  \path (A/left) -- (A/right) node [my midway label] {Case 1};

  \draw[blue] (A/left) -- (A/right);
  \draw[red]  (A/left) -- (A/right/up/1.west);
  \draw[red]  (A/left) -- (A/right/down/1.west);

  %% case 2
  \node[anchor=east] (B/left)         at ($(A/right)+(1in,0)$) {$x$};
  \node[anchor=west] (B/right)        at ($(B/left)+(1in,0)$)  {$x$};

  \path (B/left) -- (B/right) node [my midway label] {Case 2};

  \draw[blue] (B/left) -- (B/right);
\end{tikzpicture}

\end{document}

enter image description here

There are other ways of doing this as suggested by @clement . But this approach will help familiarize yourself with some basics of TikZ.

I'll explain a few of the details here:

node syntax

\node[<optional arguments>] (<optional node name>) at (<position>) {<content>};

The one part of this syntax that you cannot omit is the content.

I use the power of the calc library to help place nodes relative to each other. That's what's happening when I write:

at ($(<previously defined node name>)+(<vector>)$)

When I opened the tikzpicture environment, I defined my own private style. This is a way of helping manage the picture. The idea is that I'm going to define a node between two points along a path and then shift it in the $y$ direction.

In this case, I used a particular instance of path syntax:

\path (<1st node name>) -- (<2nd node name>) node[<optional argument] {<content>};

Note that in this case node is not a control sequence but just a bare word.

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    +1 for the long vary gracious tikz introduction for a newbie. Commented Apr 29, 2015 at 0:16

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