This script lives in /reg/g/psdm/tutorials/examplePython/mpiGather.py and demonstrates how to save small pieces of information on every event (in parallel) and then gather those pieces together onto one core.
#run this with: mpirun -n 2 python mpiGather.py
from psana import *
import numpy as np
ds = DataSource('exp=xpptut15:run=54:smd')
det = Detector('cspad',ds.env())
from mpi4py import MPI
comm = MPI.COMM_WORLD
rank = comm.Get_rank()
size = comm.Get_size()
intensity = []
for nevent,evt in enumerate(ds.events()):
img = det.image(evt)
if nevent%size==rank: # different ranks look at different events
intensity.append(img.sum())
if nevent==3: break
allIntensities = comm.gather(intensity) # get intensities from all ranks
if rank==0:
allIntensities = np.concatenate((allIntensities[:])) # put in one long list
print allIntensities
MPI.Finalize()
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