New on the IBM developerWorks, there's an article looking at using the Scilab software integrated into PHP to perform some more complicated mathematical processing.

Scripting languages like Ruby, Python, and PHP power modern-day server-side Web development. These languages are great because you can easily and rapidly build Web sites. However, their downfall is their inefficiency with complicated algorithms, such as those found in mathematics and the sciences. [...] In this article, we'll investigate one particular way to merge the power of a particular bit of scientific software - Scilab - with the ease of development and Web-friendliness of a server-side language: PHP.

Your script uses the Scilab tool from the command line, called via something like exec, and parsing the output to spit the results back out to the viewer. They show how to create two pages with form elements for allowing the user to interact with the script and one that helps you generate a graph based on some results.