On my Mac I was using LaTeXit. It takes a LaTeX code and produces instant pdfs (or pngs, jpgs, etc…).
I'm sure there's a similar programme for Ubuntu. But I was unable to find one.
Thanks in advance, Markus.
The equivalent application should be KLatexFormula, which can be installed by
sudo apt-get install klatexformula
But if you have a recent enough Ubuntu, the current version (3.2.7) triggers a bug that makes it unusable, which is fixed in 3.2.8, but it is not available at this date.
You can probably compile it from source following the instructions, I have not tried.
I have submitted a bug report.
UPDATE --- there is already (two hour after the filing of the bug!) a fix filed for Trusty that should fix the problem. Thanks to the developer.
For the sake of completion, a few more LateX equation editors:
Laeqed - LaTeX equation editor specifically targeted at producing PNG images of math equations for use on web pages. Java based, you can either download the jar file or run it directly in your browser.
Online LaTeX Equation Editor - PHP based WYSIWYG equation editor accessible with a web browser, no need to install software. Export to several different image formats including vectors.
TeXMaths - an extension to LibreOffice, only recommended if you use this office suite.