hi chuck, do you have anywhere youd recommend to get started with surgical sims (bone, flesh etc)?

Any help will be appreciated with getting start with surgical sims.

I will probably do that when I will talk about the new paper.

Right, I used edges because the method is easier to understand and implement. The visual difference is not significant. I might do a tutorial on the neo-hookean model as well.

I'm also trying to implement this on the GPU, but have problems with stability and especially energy conservation (eg. if th bunny is dropped it bounces higher and higher). Could you explain why you think that multi-color GS is like a multi-pass Jacobi solver? I don't see why it would be any different from serial GS since all the constraints solved in one pass are unrelated.

Ah I think I get it after seeing another tutorial on this. In the distance constraint, the gradient n is a unit vector so the length squared is 1.

In the case of a distance constraint the lengths of the gradients are 1. I use the sqrt to compute the gradients. In the denominator of lambda, the lengths of the gradients don't appear for the distance constraint because they are one. For the volume constraint you see that I use vecLengthSquared

@@TenMinutePhysics Thanks :) Are the derivations for the gradients of the C functions anywhere?

help me

Give it a try and let me know!

Hi Matthijs - it is being used in the gaming and film industry. Vellum, a physics engine for houdini is based on it for instance. Check it out, it is pretty cool :-) But yes, I think it could be interesting for researchers outside those industries. That is why I created this channel.

The fundamental drawback is that this modeling approach is not based on physical laws. In contrast, the continuum models are based on laws like conservation of mass and conservation of momentum. Therefore if the continuum model equations are discretized and solved accurately, the simulation result will satisfy the underlying physical laws. This is an important property for accurate prediction in real-world engineering applications. In games and films, satisfying physical laws is less important and therefore I can see why this simpler approach is valuable.

@@MichaelDodd1 I wasn't talking about real world engineering applications

I sort of solved it. According to tutorial 16 "Simulating on the GPU", a good "magic value" for averaging the corrections is 1/4. But this was not enough to maintain stability. Instead, I'm using 1/#adjacent constraints (to get the average correction over all of the adjacent constraints). Now the simulation doesn't explode (even with a 0 compliance) but (as is stated in the notes), momentum conservation is violated which causes the bunny to slide and start spinning like a figure skater eventually spinning out of control. Maybe this can be improved by damping the velocity?

@@oostenjadenhtv Hi, I'm also trying to implement this on the GPU in Unity for a uni project. I'm wondering if you managed to get a good simulation without momentum/energy conservation problems. I'm implementing it with the GS colouring method so I'm not applying corrections, but I get the bunny bouncing higher and higher. Do you know what could be the cause of this. Since you're applying corrections, I assume you're using Jacobi.

I'm also surprised that your simulation explodes for low compliance, as I have the opposite problem. For high compliances the bunny gains a lot of velocity very quickly.

Sorry for reviving your old comment but it got me curious.. It doesn't matter because the initial inverse masses for each particles are 0 here (initPhysics is called in the constructor right after creating the empty array for inverse masses). He used the "+=" operator but it's only a basic assignation so using "=" would have the same effect in this case.

@@alexisdupuis5616, not really. It is true for the first tet, but then, as vertices are shared by other tets, it is no more the case. Take a pyramid with a square base for example. It is made of 2 tets, and 3 of the 5 vertices are shared by the 2 tets. So, when you compute the first tet volume, it is working... but for the second, it is no more working for the 3 shared vertices... that is why there an initialization to 0 and then a +=.

@@crouette Oh yeah I missed that. I think you're right then because the logic would be to have the inverse mass get smaller when the vertex is present in multiple tets, I guess (?)

No, they will always flip back due to the volume constraint. You can check the demo

@@matthimf Ah, because the gradient direction!

I will show that in upcoming tutorials

@@TenMinutePhysics Is that tutorial online now?

@@jelenalukic268 help me

@@TenMinutePhysics Hello Matthias. Firstly, huge fan of your simplicity. Can you point us out, how exactly were you able to get "tetIds": [],"tetEdgeIds": [],"tetSurfaceTriIds":[] from the obj file. The obj file from Blender simply gives face ids as "f 39//1 33//1 31//1 278//1" or some other numbers which is vertex ID// normal ID, but how to identify which vertices make the tetrahedral?? What was your regex like, when you tried to parse obj to JSON??

@@abhisheksinha3074 I am glad you like it. I hacked a script to converge the meshes generated by the tetmaker. I might put it online ifI find it again :-)