User Force F(x, y, z, t)

[Chaggge]

Hello, neks!
I want to add my force which looks like this in fortran:

      if (istep.lt.1000) then
            ffy = 3*exp(-20*(y-1.0)**2-20*(x-1.0)**2-20*(z)**2)
     &      -3*exp(-20*(y+1.0)**2-20*(x-1.0)**2-20*(z)**2)
      endif

How can i do this in nekRS? As I understood I need to load kernel in oudf file as in the example:

@kernel void myForcingKernel(const dfloat dp_dx, /* more parameters */)
{
  double foo = 2 * dp_dx;

  // do something
}

But how does function look like, when I use x, y, z? And how can I refer to the time step?

[Chaggge]

If I write like this, is it ok?
UDF file:

void userf(nrs_t *nrs, dfloat time, occa::memory o_U, occa::memory o_FU)
{
  mesh_t* mesh = nrs->mesh;
  const auto fieldOffsetByte = nrs->fieldOffset * sizeof(dfloat);
  myForceKernel(
    mesh->Nlocal, 
    nrs->fieldOffset, 
    nrs->mesh->o_x,
    nrs->mesh->o_y,
    nrs->mesh->o_z,
    o_FU);
}

OUDF file:

@kernel void myForce(const dlong Ntotal,
                      const dlong offset,
                      @restrict const dfloat * X, 
                      @restrict const dfloat * Y, 
                      @restrict const dfloat * Z,  
                      @restrict dfloat * OUT) 
{
  for(dlong n=0;n<Ntotal;++n;@tile(p_blockSize,@outer,@inner)){
    if(n<Ntotal){
      const dfloat x    = X[n];
      const dfloat y    = Y[n];
      const dfloat z    = Z[n];
      
      if(isOutputStep < 1000){
        OUT[n + 0*offset] = 3 * exp(-20 * (y - 1.0)**2 - 20 * (x - 1.0)**2 - 20 * (z)**2) - 3 * exp(-20 * (y + 1.0)**2 - 20 * (x - 1.0)**2 - 20 * (z)**2);
      }
      else{
        OUT[n + 0*offset] = 0.0
      }
      OUT[n + 1*offset] = 0.0;
      OUT[n + 2*offset] = 0.0;
    }
  }
}