Thanks Alastair (@usefuldesign)

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 :

So basically
• 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
• etc

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

The code part I used is :

r1 = 125;
r2 = 125;
m1 = 10;
m2 = 10;
a1 = PI / 2;
a2 = PI / 2;
a1_v = 0;
a2_v = 0;
g = 1;
 
a1_a = ((-g*(2*m1+m2)*sin(a1))+(-m2*g*sin(a1-2*a2))+(-2*sin(a1-a2)*m2)*(a2_v*a2_v*r2+a1_v*a1_v*r1*cos(a1-a2)))/(r1*(2*m1+m2-m2*cos(2*a1-2*a2)))
 
a2_a = ((2*sin(a1-a2))*(((a1_v*a1_v*r1*(m1+m2)))+(g*(m1+m2)*cos(a1))+(a2_v*a2_v*r2*m2*cos(a1-a2))))/(r2*(2*m1+m2-m2*cos(2*a1-2*a2)))
 
a1_v += a1_a;
a2_v += a2_a;
a1 += a1_v;
a2 += a2_v;
 
x1 = r1 * sin(a1);
y1 = r1 * cos(a1);
x2 = x1 + r2 * sin(a2);
y2 = y1 + r2 * cos(a2);
 
// a1_v *= 0.99;
// a2_v *= 0.99;

The part I can't get to transcode to Vuo is

a1_v += a1_a;
a2_v += a2_a;
a1 += a1_v;
a2 += a2_v;

Cheers
PS : please guys don't make fun of my code-to-vuo transcription, I'm not a coder haha ;)