Rapidly find the points lying inside a cut-off radius

Say, in applications such as Molecular Dynamics, you may be required to find out which atoms lye within a cut-off radius (for example, the Van-der Waals distance of interaction, or say that interaction distance for the Tersoff Brenner Potential, etc..).

In any other applications, you may be required to identify a set of points lying within a circle.

This code helps you do that job, very fast. This code is completely vectorized and is fast.

Please try the code testrun.m to know how to use this code. Thank you.