How to access the information with the GPU API in EDEM?

Question

Hi, in my EDEM simulation, i want to delete particles with particular IDs, which are read from a csv file. I have successfuly implemented this function in the cpu mode (delete particles in externalForce).  But when I change to gpu mode, the particles cannot be deleted, and I do not know how to transfer the should be deleting IDs to GPU code. Can anyone tell me how to implement this function in gpu code?

Stephen Cole · Answer

Hi,

In the tutorial it doesn't use the particle.markForRemoval(); function, rather it uses the particle.markParticleOfInterest() option and processes that on the CPU.  I realise though that the markforremoval function is now avalabile on GPU (it wasn't when the tutoiral is written) but it maybe that you need to use the latest version.

It's also a good option to try and debug GPU code if it's not working as expected.  You need to use —no-free and printf()

https://help.altair.com/edem/topics/gpu_cuda_guide/debugging_gpu_cuda_t.htm

e.g.

real3 test1 = F_total_n;
printf("test1.x = %f 
", test1.x );
printf("test1.y = %f 
", test1.y ); 
printf("test1.z = %f 
", test1.z );

ou could use this to check what ID is been passed to the code.

llu · Answer

Thanks for the reply.

I have read this tutorial, but it can not solve my problem. i need to read the csv during the simulation. The csv is generated by another UDL, thus I can not read the particles id at the setup function.

What I want to do is to find some particles and delete them. I can implement this function in CPU mode: find particles and delete them in factory UDL. However, in GPU mode, it did not work. the markForRemoval function has no effect on GPU mode. I then tried to mark the particles by setScale=10 in factory UDL and then delete them in  externalForce. It works in CPU mode, but in GPU mode, it fails, it seems the setScale has no effect on GPU mode.

In .cu file, the code is:

if (particleScale > REAL_CONST(1.5) || massScale > REAL_CONST(1.5))

{

particle.markForRemoval();

return;

}

in .cpp code, the code is:

if (particleScale > 1.5 || massScale > 1.5)

{

m_particleManager->markForRemoval(particle.ID);

Stephen Cole · Answer

Hi,

The code in this tutorial uses the particle.markParticleOfInterest(); function on the GPU .cu code.  This means the particle is then passed to the CPU which can then delete them. This is done in processParticleOfInterest part of CRemoval.cpp.

https://community.altair.com/discussion/39783/edem-api-4000-api-introduction-particle-replacement

You could use the same part of the code to write to a file, though I would generally avoid writing to a file during simulation as you can run into threadsafe issues.

Regards

Stephen