To: Nils Wagner <nwagner@...56...>

Cc: SciPy Users List <scipy-user@...29...>,

matplotlib-users@lists.sourceforge.net

Subject: Re: [Matplotlib-users] Visualizing Sparsity Pattern of matrices

From: John Hunter <jdhunter@...4...>

Date: Thu, 11 Nov 2004 09:16:03 -0600"Nils" == Nils Wagner <nwagner@...56...> writes:

> Hi all, Structure plots provide a quick visual check on the

> sparsity pattern of the matrix. A structure plot is a

> rectangular array of dots; a dot is black if the

> corresponding matrix element is nonzero otherwise it is

> white.> Is it possible to generate such plots with scipy or should

> we switch over to matplotlib ?Here's another implementation that uses images - likely to be much

faster for very large matrices.

Hi,

As part of a programming environment for optimization in Python (soon to be released hopefully), I use Matplotlib for the graphics. I created several functions imitating Matlab's spy() using scatter(). My sparse matrices are represented in linked-list, compressed column or compressed row storage using the PySparse implementation

http://people.web.psi.ch/geus/pyfemax/pysparse.html

Using scatter, I can plot the sparsity pattern of matrices with several thousands of lines and columns in a blink on my 1.7GHz P4 laptop. Using color maps, you can even color your dots according to the magnitude of the element they represent (a 2-dimensional "city plot" of a matrix).

Dominique