sympy/sympy — pull request #1426 by scolobb (2012-07-18 11:13:27+00:00)
Title: sympy.printing.preview: Support additional LaTeX packages.

This commit adds the keyword argument `packages` to `preview` which should be a list of LaTeX package names to be added to the preamble of the document.

I need this modification to be able to use `preview` with diagram drawing functionality, which requires the inclusion of `xypic` package in the preamble of the LaTeX document.