import mesh with mpi, without partition it

Question

Hi there,

Fenics 2016.1 with mpi

So, when we want to create mesh to be used later to solve independent problems we use mpi_comm_self (then one mesh for each process):

if rank_process==0:
    mesh = UnitSquareMesh(mpi_comm_self(), 10, 10)
if rank_process==1:
    mesh = UnitSquareMesh(mpi_comm_self(), 20, 20)

Then, what is the syntax when i import a mesh (without partition it!)

In a first program (that runs in serial without mpi) i have created a mesh and its meshfunction

mesh_= BoxMesh(Point(0.0, 0.0, 0.0), Point(length_0, length_1, length_2), n_0, n_1,n_2)
subdomains_ = MeshFunction('size_t', mesh_, 3)

Then i have marked it

class OmegaA(SubDomain):
    def inside(self, x, on_boundary):
    ....
OmegaA().mark(subdomains_ , id_A)       
OmegaB().mark(subdomains_ , id_B)

and then i have saved it:

File(Folder_Mesh_fenics + 'mesh.xml.gz') << mesh_
File(Folder_Mesh_fenics + 'mesh_function.xml.gz') << subdomains_

Now, i want I want to import mesh.xml.gz and mesh_function.xml.gz in a program with mpirun.
If i use the classic import symtax

mesh = Mesh(filepath)

Then the mesh is partitioned. I don't want this. I want to keep it unpartitioned.

# Instead of this:
mesh = Mesh(filepath_DOMAIN)
# Something like this:
if rank_process==0:
    mesh = Mesh(mpi_comm_self(),filepath)  # Does not work
if rank_process==1:
    mesh = Mesh(mpi_comm_self(),filepath) # Does not work

If you wander why, i want to run independent calculation on the two subdomain (using submesh)
PS: i already know submesh with mpi is not immediate to get, for what i have read in the forum -> this will be my next issue. For now, i just want to get correctly the import.

Thanks for any help.

fussegli · Answer 1 · Apr 15, 2017

The code i have written works actually...

if rank_process==0:
    mesh = Mesh(mpi_comm_self(),filepath)

is the good syntax (i thought it would not work) to import the mesh.

answered Apr 15, 2017 by fussegli FEniCS Novice (700 points)

However,

subdomains_ = MeshFunction('size_t', mesh, filepath_functions)

and

subdomains_ = MeshFunction(mpi_comm_self(),'size_t', mesh, filepath_functions)

do not work...
Any idea?

EDIT: once i can import subdomains_ i will try
https://fenicsproject.org/qa/7203/mpi-submesh-and-partitioning?show=7203#q7203

from cbcpost.utils import create_submesh
submesh_A = create_submesh(mesh, subdomains_, id_A)
submesh_B = create_submesh(mesh, subdomains_, id_B)

commented Apr 15, 2017 by fussegli FEniCS Novice (700 points)

import mesh with mpi, without partition it

1 Answer