Send and receive specific parts mpi

Question

I've got a problem regarding my code. I want this code to send elements of an array to certain workers. The workers 0-7 should receive 12, 18, 30, 36, 48, 54, 66, 72. So I used send and receive in order to do that but when I execute my code I just get to part 66 but not 72. So there is one missing and it does not start at 0. Maybe you can help me.

Here is my code:

import numpy as np
import pandas as pd
from mpi4py import MPI

comm = MPI.COMM_WORLD
rank = comm.Get_rank()
size = comm.Get_size()

a=np.random.rand(336,1) #array
sizedarray=[]
starting_point=0
ending_point=12
sizes=[]
q=[]
if rank == 0:#masterrrank
    for i in range(0,size-1):
    
        take_out=0
        sizedarray.append(a[starting_point:ending_point])
        starting_point=ending_point
        if i % 2 == 0:
            ending_point= ending_point + len(sizedarray[i]) + 6
            sizes.append(len(sizedarray[i]))

            
        elif i % 2 !=0:
            
            ending_point=len(sizedarray[i]) +12+ ending_point
            sizes.append(len(sizedarray[i]))
        
        comm.send(a[take_out:sizes[i]+take_out],dest=i+1)
        take_out=take_out+sizes[i]    


else:  
    p=comm.recv(source=0)
    
    print(len(p),"    ", rank)

and my outcome:

Yes that was what i thought, is there a way to send it to himself? — Thorte, May 14 '20 at 13:02
one option is to not send it but simply `p=a[take_out:sizes[i]+take_out]`. if you want to send it, beware of deadlock; you can use `sendrecv()` or non blocking `isend()` and/or `irecv()` (and `wait()` for the request to complete). — Gilles Gouaillardet, May 14 '20 at 14:24
fwiw, your program is a textbook implementation of `scatterv()` — Gilles Gouaillardet, May 14 '20 at 14:44
i hope so, check https://stackoverflow.com/questions/39329492/how-to-scattering-a-numpy-array-in-python-using-comm-scatterv — Gilles Gouaillardet, May 14 '20 at 14:47
If i dont send it, not every worker gets a certain size right? — Thorte, May 14 '20 at 14:50
Let us [continue this discussion in chat](https://chat.stackoverflow.com/rooms/213869/discussion-between-thorte-and-gilles-gouaillardet). — Thorte, May 14 '20 at 16:28

Send and receive specific parts mpi

0 Answers0