Vector arrays

[cyrush]

Discussed in #1328

^{Originally posted by yslan July 10, 2024}
Hi,

I wonder what's the proper way to pass a vector field to Ascent.

• 3 scalars
  I know we can break it into scalars like this.

        mesh_data["fields/velocity_x/association"] = "vertex";
        mesh_data["fields/velocity_x/topology"] = "mesh";
        mesh_data["fields/velocity_x/values"].set_external((dfloat *)o_u.ptr(), N);
        
        mesh_data["fields/velocity_y/association"] = "vertex";
        mesh_data["fields/velocity_y/topology"] = "mesh";
        mesh_data["fields/velocity_y/values"].set_external((dfloat *)o_v.ptr(), N);
        
        mesh_data["fields/velocity_z/association"] = "vertex";
        mesh_data["fields/velocity_z/topology"] = "mesh";
        mesh_data["fields/velocity_z/values"].set_external((dfloat *)o_w.ptr(), N);        
  

  And, we can composite back to vector in ascent_actions.yaml
  This approach is robust and well-tested in my code.

• vector
  I've also managed to send the vector like this (Is this the correct way?).

        mesh_data["fields/velocity/association"] = "vertex";
        mesh_data["fields/velocity/topology"] = "mesh";
        mesh_data["fields/velocity/values/u"].set_external((dfloat *)o_u.ptr(), N);
        mesh_data["fields/velocity/values/v"].set_external((dfloat *)o_v.ptr(), N);
        mesh_data["fields/velocity/values/w"].set_external((dfloat *)o_w.ptr(), N);
  

  Then, from vector, it can extract components in ascent_actions.yaml

• Can we have both?
  The question occurs when I have both vector and 3-scalars implementation with the same pointer.
  The idea is to keep "vector of arrays" structure, but also make sure both vector and scalar components are visible in ascent_actions.yaml, which saves a lots of conversion.
  This works when I run it on CPU backend but it gets SEGV when running with GPU. Both CPU and GPU are tested on Polaris.

I appreciate any suggestions.

Thanks,
Yu-Hsiang

[cyrush]

Second case (presented as a vector field directly) is crashing for GPU case.