Please enter an algebraic expression without any surrounding $$ into the text box below. (Click here for help.)

First a brief overview of how the TeX filter works. The TeX filter first searches the database cache_filters table to see if this TeX expression had been processed before. If not, it adds a DB entry for that expression. It then replaces the TeX expression by an <img src=".../filter/tex/pix.php..."> tag. The filter/tex/pix.php script then searches the database to find an appropriate gif image file for that expression and to create one if it doesn't exist. Here are a few common things that can go wrong and some suggestions on how you might try to fix them.

1. Something had gone wrong on a previous occasion when the filter tried to process this expression. Then the database entry for that expression contains a bad TeX expression in the rawtext field (usually blank). You can fix this by clicking on "Delete DB Entry"
2. The TeX to gif image conversion process does not work. If your server is running Unix, a likely cause is that the mimetex binary you are using is incompatible with your operating system. You can try compiling it from the C sources downloaded from http://www.forkosh.com/mimetex.zip, or looking for an appropriate binary at http://moodle.org/download/mimetex/. You may then also need to edit your moodle/filter/tex/pix.php file to add
   case "Linux":
   to the list of operating systems in the switch (PHP_OS) statement. Windows users may have a problem properly unzipping mimetex.exe. Make sure that mimetex.exe is is PRECISELY 433152 bytes in size. If not, download a fresh copy from http://moodle.org/download/mimetex/windows/mimetex.exe. Another possible problem which may affect both Unix and Windows servers is that the web server doesn't have execute permission on the mimetex binary. In that case change permissions accordingly