You mean the concept of a sparse matrix ? Well, for e.g. if you use FEM (Finite Element method) you usually end up with a huge linear system which has the nice property that more than 90% of his coefficients are zeros. A sparse matrix will store only the non-zero elements, this is a huge gain from the point of view of memory usage.

Similar considerations applies for using Finite Difference methods.

They are also at the heart of the SPICE circuit simulator[1]

[1] http://en.wikipedia.org/wiki/SPICE#Introduction

Although for finite difference schemes we dont usually form the matrix but rather perform convolution/ forward stencil math.

I used it for testing Spare Matrix kernels I wrote for my Uni thesis.

However, god knows why this site is considered news worthy. I mean it's the same as it was yesterday, and the day before...

It's really useful for testing FEA algorithms/code. Tim Davis has done a ton of work developing numerical algorithms for sparse systems, his code is used by software like MATLAB and also bespoke supercomputer systems.

Thanks guys