dragonfly_sim.utils.mpi_utils
=============================

.. py:module:: dragonfly_sim.utils.mpi_utils


Functions
---------

.. autoapisummary::

   dragonfly_sim.utils.mpi_utils.allgather_numpy
   dragonfly_sim.utils.mpi_utils.assign_global_dof_offset


Module Contents
---------------

.. py:function:: allgather_numpy(comm, local_arr, global_size)

   
   Allgatherv a rank-local float64 array into a global array on every rank.

   Each rank contributes a (possibly different-length) slice of the global
   array.  The slices are ordered by rank: rank 0 occupies [0, len_0),
   rank 1 occupies [len_0, len_0+len_1), etc.  This ordering matches the
   contiguous DOF blocks produced by ``assign_global_dof_offset``.

   :Parameters:

       **comm** : mpi4py.MPI.Comm
           ..

       **local_arr** : array-like, float64, 1-D
           The local contribution on this rank.  Cast to C-contiguous float64
           before sending.

       **global_size** : int
           Total number of float64 elements summed across all ranks.  Must be
           the same value on every rank.



   :Returns:

       np.ndarray, float64, shape (global_size,)
           The gathered array, identical on every rank.











   ..
       !! processed by numpydoc !!

.. py:function:: assign_global_dof_offset(comm, local_count)

   
   Compute the global DOF offset for this rank via exclusive prefix-sum.

   Assigns a contiguous block of global indices to each rank:
       rank 0 → [0,                    local_count_0)
       rank 1 → [local_count_0,        local_count_0 + local_count_1)
       ...

   Implementation uses MPI ``Exscan`` (exclusive scan with SUM) to
   compute the offset for each rank in a single collective, then
   ``Allreduce`` on a scalar to obtain the global total.  This avoids
   allocating an N-rank array and is the canonical MPI pattern for
   assigning contiguous global index ranges to processes.

   :Parameters:

       **comm** : mpi4py.MPI.Comm
           ..

       **local_count** : int
           Number of local DOFs on this rank.



   :Returns:

       **offset** : int
           Index of the first global DOF owned by this rank.

       **global_total** : int
           Total DOF count across all ranks.











   ..
       !! processed by numpydoc !!