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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.

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

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

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

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