Yeah that's how I somehow understood it too when googling it.
Trying to transcode this sign to Vuo with for example a1 += a1_v I got something like :
• take the first value of "a1", put it the 1st port of "the Select Latest node and add this to "a1_v"
• I hold this new value of "a1", which now becomes the latest value and add "a1_v" to it again
Joining latest comps if anybody wants to join ;) I can't get my wrap around it, probably doing nonsense here ;)
Regarding the Double Pendulum man I tried to recreate that but without luck so far.
I just don't really understand how to transpose the += sign from the processing code maybe. Or maybe I'm thinking it's too easy and requires deeper calculations.
I either get a not really moving pendulum or a perfectly mirrored drawing esoteric butterflies pendulum ;)
Posting the files here if some math superhero want to help you achieving this :) I guess for a math/coder it should be easy.
Anyway, the code as Martinus suggested is from : Double Pendulum coding challenge #93
No I haven't played with it anymore, not sure how far you can put the shader working with the "Reinterpret 3D Object" node, guess it would be better to use Karl's "Make Mesh With Values" node but as I said, am not very skilled when it comes to meshes.