TraerParticleSystem

Extension

Construct a new particle system with some downward (positive y) or 3D gravity and some drag. You can make as many of these as you'd like as long as forces from one system don't refer to particles from another. I don't know what would happen if you connected particles from one system to another.

pass this either: \RUNGE_KUTTA or \MODIFIED_EULER as a Symbol.

Discussion:

Runge-Kutta is the default. It takes about 4 times as many cycles as Modified Euler. In return the system gets very stable. If you plan to have have over 1000 particles interacting with each other try Modified Euler. If you will have fewer particles and want tight springs and quicker responses use Runge-Kutta. Stick with the default and if things get slow try switching to Euler. You may have to add more drag or reduce the strength of springs and attractions to keep it stable. The example Random Arboretum has sections of code you can uncomment to experiment with this.

set the strength of gravity, down (in the positive y direction) or in whatever 3D direction you feel like. You probably want the magnitude of this to be in the range of 0-5.

set the drag force that acts on all objects equally, and proportional to velocity.

advance the simulation by some time t, or by the default 1.0. You'll want to call this in UserView: -drawFunc or Window: -drawFunc. You probably want to keep this the same at all times unless you want speed up or slow things down.

this deletes all the particles and all the forces in the system (except the omnipresent gravity and drag even if there are 0).

Create a new particle in the system with some mass and at some x, y, z position. The default is a new particle with mass 1.0 at (0, 0, 0).

make a spring in the system between 2 particles you have previously created. Look at TraerSpring for what the parameters mean.

Make an attraction (or repulsion) force between two particles. If the strength is negative they repel each other, if the strength is positive they attract. There is also a minimum distance that limits how strong this force can get close up.