Getting neighbours in a VOP POP

[simonj]

I have a couple of questions regarding particles, vop pops and expressions. Any answers are greatly appreciated.

1st question -

If I have a bunch of particles emitting from a Source node, then plugged into a VOP POP node, how can I, inside the VOP POP node, access each points neighbors and for example get their velocity. I know how I can use a Proximity node to set $NEAREST, $NEARESTDIST and $NUMPROXIMITY, but how do I access these attributes inside of the VOP POP network, or should I use the Neighbor and Neighbor Count - nodes in some way? Because I haven't got that to work.

2st question -

Since I'm a programmer at heart, I'd love to start learning some heavier programming in Houdini, but I don't really know how to implement and work with scripts, I've seen simple examples of code (like code looping through all points in a specific geometry and affecting them) when searching around these forums, but where and how do you make these run each frame? Is there a specific script-node I've missed, or are these scripts just put inside parameters?

3rd and last question -

Any general tips in the learning process of Houdini, I've already gone through two "fundamentals of Houdini"-type video tutorials. But any other "must haves" out there, particularly about the scripting parts?

Thanks for any time and answers given to these questions.