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LaTeX Equations and Graphics in PHP

Issue 131

From Issue #131
March 2005

Jan 26, 2005  By Titus Barik
 in
Make the difficulties of displaying mathematical equations on the Web a thing of the past by embedding LaTeX content in your pages.

When Things Go Awry

If something goes wrong at the rendering stage, you can try to process a LaTeX file manually by using the shell with the following commands for diagnostics: 

latex --interaction=nonstopmode my.tex
dvips -E my.dvi -o my.ps
convert -density 120 my.ps my.png

This allows you to isolate the specific step at which the LaTeX renderer fails.

cleanup Method

During the LaTeX rendering process, a large number of temporary files are created. This cleanup method deletes these extraneous files, and there's really not much to it, as shown in Listing 5.

Listing 5. cleanup.php 

function cleanup($hash) {

  $current_dir = getcwd();
  chdir($this->TMP_DIR);

  unlink($this->TMP_DIR . "/$hash.tex");
  unlink($this->TMP_DIR . "/$hash.aux");
  unlink($this->TMP_DIR . "/$hash.log");
  unlink($this->TMP_DIR . "/$hash.dvi");
  unlink($this->TMP_DIR . "/$hash.ps");
  unlink($this->TMP_DIR . "/$hash.png");

  chdir($current_dir);
}
transform Method

The transform method, shown in Listing 6, drives the rendering class and provides a public access point for the programmer.

Listing 6. transform.php 


function transform($text) {

  preg_match_all("/\[tex\](.*?)\[\/tex\]/si", $text, $matches);

  for ($i = 0; $i < count($matches[0]); $i++) {

    $position = strpos($text, $matches[0][$i]);
    $thunk = $matches[1][$i];

    $hash = md5($thunk);
    $full_name = $this->CACHE_DIR . "/" .
                 $hash . ".png";
    $url = $this->URL_PATH . "/" .
           $hash . ".png";

    if (!is_file($full_name)) {
      $this->render_latex($thunk, $hash);
      $this->cleanup($hash);
    }

    $text = substr_replace($text,
      "<img src=\"$url\" alt=\"Formula: $i\" />",
      $position, strlen($matches[0][$i]));
  }

  return $text;
}

The preg_match_all function in PHP extracts the thunks as well as the positions of each thunk. Each thunk then is parsed individually through the loop. Next, a unique md5 of the thunk text is created. This tells us whether a thunk has been cached before. If the thunk has not been cached, I call the LaTeX renderer method and immediately clean up the resulting temporary files. In either case, the thunk is substituted with a URL. When all thunks are processed, the text is returned.

Equation Examples

Now, let's look at a few examples that illustrate the kinds of equations you can render with the help of LaTeX. Most of these equations are taken from A Guide To LaTeX by Helmut Kopka and Patrick W. Daly, considered by many to be one of the essential books on the LaTeX system.

Figure 2. Example: Fractions 


[tex]
\begin{displaymath}
\frac{a^2 - b^2}{a + b} = a - b
\end{displaymath}
[/tex]

Figure 3. Example: Correlation of Two Variables, X and Y 


[tex]
\begin{displaymath}
\mathop{\mathrm{corr}}(X,Y)=
\frac{\displaystyle
\sum_{i=1}^n(x_i-\overline x)
(y_i-\overline y)}
{\displaystyle\biggl[
\sum_{i=1}^n(x_i-\overline x)^2
\sum_{i=1}^n(y_i-\overline y)^2
\biggr]^{1/2}}
\end{displaymath}
[/tex]

Figure 4. Example: A More Complex Equation 


[tex]
\begin{displaymath}
I(z) = \sin( \frac{\pi}{2} z^2 ) \sum_{n=0}^\infty
    \frac{ (-1)^n \pi^{2n} }{1 \cdot 3 
    \cdots (4n + 1) } z^{4n + 1}
    -\cos( \frac{\pi}{2} z^2 ) \sum_{n=0}^\infty
    \frac{ (-1)^n \pi^{2n + 1} }{1 \cdot 3 
    \cdots (4n + 3) } z^{4n + 3}
\end{displaymath}
[/tex]

______________________

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Another aproach to LaTeX equations with PHP

Filipi Vianna's picture
Submitted by Filipi Vianna (not verified) on Mon, 04/06/2009 - 16:33.

Some time ago I had faced the same problem, but I didn't use the same rendering steps. Instead of rendering to PS and then converting to PNG, I had used dvipng to convert the DVI directly to PNG.

The code is at my personal blog.

Hope it also helps somebody.

Regards,
Filipi Vianna

A bit of trouble

Skylar Saveland's picture
Submitted by Skylar Saveland (not verified) on Sat, 11/08/2008 - 14:52.

I have been looking for something like this off and on for months but I am a programming newb with most experience in python; this article has me crash-coursing php.

I think I am having problems naming the .php files, placing them in the right place and/or setting the correct permissions. I know exactly where convert, latex and dvips are, that is not the problem. I have put everything in the document root in separate files, each listing.

wrap.php7870l3.qrk I have just named wrap.php, I can't find any logic for the '7870l3.qrk' part.

If I name the second listing/file 'render.php' I get the follwing error:
Warning: require(render.class.php) [function.require]: failed to open stream: No such file or directory in /var/www/render_example.php on line 26

Fatal error: require() [function.require]: Failed opening required 'render.class.php' (include_path='.:/usr/share/php:/usr/share/pear') in /var/www/render_example.php on line 26

If I name the second listing 'render.class.php' I get a different error:
class render { var $LATEX_PATH = "/usr/bin/latex"; var $DVIPS_PATH = "/usr/bin/dvips"; var $CONVERT_PATH = "/usr/bin/convert"; var $TMP_DIR = "/usr/home/biouser/texwebtmp"; var $CACHE_DIR = "/usr/home/biouser/texwebtmp/cache"; var $URL_PATH = "http://127.0.1.1/lj/cache"; function wrap($text) { ... } function transform($text) { ... } function render_latex($text) { ... } }
Fatal error: Class 'render' not found in /var/www/render_example.php on line 33

Something is going on here... I would b so excited and grateful if i could get this to work!!!

uninformed question

matt's picture
Submitted by matt (not verified) on Thu, 09/25/2008 - 12:26.

This looks exactly like what I need. I am trying to set up a simple wiki to collaborate with co-writers, and am trying to find how to embed latex capabilities. I am a rookie in programming though, and cannot figure out some things. Specifically, "You need to let PHP know where your tools are located and provide a directory where PHP can write temporary files and store its cache."==> What tools? I see I need latex and dvips etc., but what exactly are these as tools? I use latex, but don't know exactly what I need to upload to the server.

Thanks!
matt

Awesome!

David Sankey's picture
Submitted by David Sankey (not verified) on Fri, 09/12/2008 - 17:06.

Hi!

I'm starting to implement this into a math worksheet website I'm (slowly) building. It's superior to html formatting because it doesn't vary from browser to browser. I had to alter it a bit because I'm making worksheets for print and the images weren't printing well. I changed the density to 300. Then, I get the image height using "identity" and reduce it by 40% using the height attribute in the image tag.

The images on screen are a bit choppy but the prints look great. My students are sure to appreciate it!

Would you like me to post a link or give you other credit?

Thanks a bunch!

Dynamic Base URL

Carlos S.'s picture
Submitted by Carlos S. (not verified) on Wed, 11/30/2005 - 06:51.

It may be a good idea to add a function to get the base URL instead of hard writing it on the source code.
it may be something like:

$base_url = 'http' . (isset($_SERVER['HTTPS']) ? $_SERVER['HTTPS'] == 'on' ? 's' : '' : '');
$base_url .= '://' .$_SERVER['HTTP_HOST'];
if ($dir = trim(dirname($_SERVER['SCRIPT_NAME']), '\,/')) {
$base_url .= "/$dir";
}
$URL_PATH= $base_url . "/cache"

Carlos

Web CAS, another LaTeX+PHP on Apache

Anonymous's picture
Submitted by Anonymous (not verified) on Wed, 03/16/2005 - 00:05.

Although I has not read the interesting article, a project of SourceForge, WMI (Web Mathematic Interactive, http://wmi.sf.net), may be the subject that readers are interested. WMI integrates almost the powerful CAS in Linux world, e.g. Maxima, Octave, Gnuplot and Maple etc. within LAMP envirnment. Don't forget to visit the official site.

Curious

summentier's picture
Submitted by summentier (not verified) on Mon, 05/15/2006 - 14:30.

How did you know that the article was interesting if you hadn't read it? I did read it and it was great help!

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