[Student_GF]

Hi All,

I have a question regarding UDF's, mainly using "first iteration".

I currently creating a UDF code to execute in the first iteration of a timestep using "first Iteration". The problem I am having is that when simulation is executed, the code that I intended to be executed at at the first iteration executes 5 times rather than the intended one in the first iteration of a time step. Does anyone know why this occurs?

Thank you.

[`e`]

What is your UDF and are you running in parallel or serial mode?

[Student_GF]

Hello!

My simulation is running in parallel woth 4 processes.

[Student_GF]

Opps currently I am not on my work computer but the code is something like the following
define Profile
{
Begin cell loop
{
if (first_iteration)
{
(does operation)
}
else
{
(default to constant value)
}
printf(Display Values <- This was done so I can determine how many time it is running at what time)
}
end Cell loop
}

If you need the real code, I can get it to you later tonight.

[`e`]

The DEFINE_PROFILE macro is called by all compute nodes and the host (in parallel mode). For your case where parallel is used with four processes, four compute nodes exist as well as the host causing the macro to be called a total of five times. Depending on what you're trying to achieve, this duplication is fine.

The cell loop (with begin_c_loop) only contains the cells on the respective compute node. If the boundary value only depends on local values on its compute node (e.g. position) then you'll be fine as is. However, if you're defining a boundary value based on global values (e.g. total volume of the computation domain) then you'll need to be careful of counting overlapping cells. Have a read of the parallel considerations chapter in the UDF manual for details (the section on looping over interior and exterior cells).