# DofMap and ghost values

**URL:** <https://fenicsproject.discourse.group/t/dofmap-and-ghost-values/11760>\
**Category:** dolfinx\
**Created:** [July 18, 2023, 9:55am UTC](https://fenicsproject.discourse.group/t/dofmap-and-ghost-values/11760 "2023-07-18T09:55:23Z")\
**Posts on this page:** 1\
**Showing post:** 3

<div class="post-metadata">

**Author:** ![dokken](https://yyz2.discourse-cdn.com/free1/user_avatar/fenicsproject.discourse.group/dokken/32/1560_2.png) [@dokken](https://fenicsproject.discourse.group/u/dokken)\
**Post date:** [July 21, 2023, 7:55am UTC](https://fenicsproject.discourse.group/t/dofmap-and-ghost-values/11760/3 "2023-07-21T07:55:10Z")

</div>

Here is an example that creates the local\_to\_global map containing both owned and unowned dofs (unrolled for block size).

```python
import dolfinx
from mpi4py import MPI
import ufl
import numpy as np
domain = dolfinx.mesh.create_unit_square(MPI.COMM_WORLD, 2, 2)
el0 = ufl.FiniteElement("Lagrange", domain.ufl_cell(), 1)
el2 = ufl.VectorElement("Lagrange", domain.ufl_cell(), 2)
el = ufl.MixedElement([el0, el2])
V = dolfinx.fem.FunctionSpace(domain, el)

u = dolfinx.fem.Function(V)

# Create local map
local_range = V.dofmap.index_map.local_range
num_dofs_local = V.dofmap.index_map.size_local
local_dof_map = np.arange(num_dofs_local, dtype=np.int64)
local_dof_map += local_range[0]

# Get ghost indices
num_ghosts = V.dofmap.index_map.num_ghosts
ghosts = V.dofmap.index_map.ghosts
ghost_ownership = V.dofmap.index_map.owners

# Unroll for block size
bs = V.dofmap.index_map_bs
local_to_global = np.zeros((num_dofs_local+num_ghosts)*bs, dtype=np.int64)
owners = np.zeros_like(local_to_global)
for i in range(bs):
    for j in range(num_dofs_local):
        local_to_global[j*bs+i] = local_dof_map[j]*bs+i
        owners[j*bs+i] = domain.comm.rank

    for j in range(num_ghosts):
        local_to_global[num_dofs_local*bs+ j*bs + i] = ghosts[j]*bs+i
        owners[num_dofs_local*bs + j*bs+i] = ghost_ownership[j]

import time
time.sleep(domain.comm.rank)
print(f"Rank {domain.comm.rank}, Block size {bs} Num local dofs {num_dofs_local*bs} Num ghosts {num_ghosts*bs}", local_to_global, owners)

```

yielding:

```bash
mpirun -n 3 python3 script.py 
Rank 0, Block size 1 Num local dofs 19 Num ghosts 17 [ 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 48 49 50 24 25
 26 27 28 31 32 19 20 21 22 23 57 58] [0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 2 2 1 1 1 1 1 1 1 1 1 1 1 1 2 2]
Rank 1, Block size 1 Num local dofs 14 Num ghosts 31 [19 20 21 22 23 24 25 26 27 28 29 30 31 32 48 1 49 50 4 5 57 58 6 7
 33 36 37 53 54 0 2 3 10 11 35 40 41 51 52 44 45 8 9 55 56] [1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 0 2 2 0 0 2 2 0 0 2 2 2 2 2 0 0 0 0 0 2 2 2
 2 2 2 2 0 0 2 2]
Rank 2, Block size 1 Num local dofs 26 Num ghosts 17 [33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56
 57 58 19 20 21 24 25 26 27 28 29 30 1 4 5 22 23 6 7] [2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1 0
 0 0 1 1 0 0]

```

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