Python: comm.Scatterv() in mpi4py, why the value changes after scattering
I want scatter different length np.array to different ranks, but I find the value changed and I do not know why.
I tried many times and simplified my code as below.
import numpy as np
import random
from random import seed
from mpi4py import MPI
comm = MPI.COMM_WORLD
size = comm.Get_size()
rank = comm.Get_rank()
num = 4
N = num // size + (num % size > rank)
position_x = np.zeros(num,dtype=float)
seed(10059)
for i in range(num):
position_x[i] = round(random.uniform(-5,5),3)
print(position_x)
if rank == 0:
share1 = position_x
else:
share1 = None
count =
for i in range(size):
if i <= num%size-1:
count += [num//size + 1]
else:
count += [num//size]
pos1 = np.zeros(N, dtype='f')
comm.Scatterv([share1, count, MPI.FLOAT], pos1, root=0)
print(pos1,'from ',rank)
The result of 3 processes is shown below.
[-2.275 4.238 -1.637 0.981]
[5177.344] from 1
[-2.275 4.238 -1.637 0.981]
[ 4.172325e-08 -2.034375e+00] from 0
[-2.275 4.238 -1.637 0.981]
[2.264875] from 2
I cannot understand where the strange numbers come from. The result should be [-2.275 4.238] from 0, [-1.637] from 1, [0.981] from 2 if right.
Does anyone have an idea? Thank you very much.
————————————————————————————————————————————
Update:
I find if the numbers in np.array are float, it will have this problem. I try to change the DATATYPE to MPI.INT or MPI.F_FLOAT, but it still doesn't work.
It seems caused by random, but I need to randomly generate the position.
I really do not know how to correct it.
python numpy mpi4py
asked Nov 19 '18 at 14:36
RunningRunning
12
add a comment |
I want scatter different length np.array to different ranks, but I find the value changed and I do not know why.
I tried many times and simplified my code as below.
import numpy as np
import random
from random import seed
from mpi4py import MPI
comm = MPI.COMM_WORLD
size = comm.Get_size()
rank = comm.Get_rank()
num = 4
N = num // size + (num % size > rank)
position_x = np.zeros(num,dtype=float)
seed(10059)
for i in range(num):
position_x[i] = round(random.uniform(-5,5),3)
print(position_x)
if rank == 0:
share1 = position_x
else:
share1 = None
count =
for i in range(size):
if i <= num%size-1:
count += [num//size + 1]
else:
count += [num//size]
pos1 = np.zeros(N, dtype='f')
comm.Scatterv([share1, count, MPI.FLOAT], pos1, root=0)
print(pos1,'from ',rank)
The result of 3 processes is shown below.
[-2.275 4.238 -1.637 0.981]
[5177.344] from 1
[-2.275 4.238 -1.637 0.981]
[ 4.172325e-08 -2.034375e+00] from 0
[-2.275 4.238 -1.637 0.981]
[2.264875] from 2
I cannot understand where the strange numbers come from. The result should be [-2.275 4.238] from 0, [-1.637] from 1, [0.981] from 2 if right.
Does anyone have an idea? Thank you very much.
————————————————————————————————————————————
Update:
I find if the numbers in np.array are float, it will have this problem. I try to change the DATATYPE to MPI.INT or MPI.F_FLOAT, but it still doesn't work.
It seems caused by random, but I need to randomly generate the position.
I really do not know how to correct it.
python numpy mpi4py
asked Nov 19 '18 at 14:36
RunningRunning
12
add a comment |
I want scatter different length np.array to different ranks, but I find the value changed and I do not know why.
I tried many times and simplified my code as below.
import numpy as np
import random
from random import seed
from mpi4py import MPI
comm = MPI.COMM_WORLD
size = comm.Get_size()
rank = comm.Get_rank()
num = 4
N = num // size + (num % size > rank)
position_x = np.zeros(num,dtype=float)
seed(10059)
for i in range(num):
position_x[i] = round(random.uniform(-5,5),3)
print(position_x)
if rank == 0:
share1 = position_x
else:
share1 = None
count =
for i in range(size):
if i <= num%size-1:
count += [num//size + 1]
else:
count += [num//size]
pos1 = np.zeros(N, dtype='f')
comm.Scatterv([share1, count, MPI.FLOAT], pos1, root=0)
print(pos1,'from ',rank)
The result of 3 processes is shown below.
[-2.275 4.238 -1.637 0.981]
[5177.344] from 1
[-2.275 4.238 -1.637 0.981]
[ 4.172325e-08 -2.034375e+00] from 0
[-2.275 4.238 -1.637 0.981]
[2.264875] from 2
I cannot understand where the strange numbers come from. The result should be [-2.275 4.238] from 0, [-1.637] from 1, [0.981] from 2 if right.
Does anyone have an idea? Thank you very much.
————————————————————————————————————————————
Update:
I find if the numbers in np.array are float, it will have this problem. I try to change the DATATYPE to MPI.INT or MPI.F_FLOAT, but it still doesn't work.
It seems caused by random, but I need to randomly generate the position.
I really do not know how to correct it.
python numpy mpi4py
asked Nov 19 '18 at 14:36
RunningRunning
12
I want scatter different length np.array to different ranks, but I find the value changed and I do not know why.
I tried many times and simplified my code as below.
import numpy as np
import random
from random import seed
from mpi4py import MPI
comm = MPI.COMM_WORLD
size = comm.Get_size()
rank = comm.Get_rank()
num = 4
N = num // size + (num % size > rank)
position_x = np.zeros(num,dtype=float)
seed(10059)
for i in range(num):
position_x[i] = round(random.uniform(-5,5),3)
print(position_x)
if rank == 0:
share1 = position_x
else:
share1 = None
count =
for i in range(size):
if i <= num%size-1:
count += [num//size + 1]
else:
count += [num//size]
pos1 = np.zeros(N, dtype='f')
comm.Scatterv([share1, count, MPI.FLOAT], pos1, root=0)
print(pos1,'from ',rank)
The result of 3 processes is shown below.
[-2.275 4.238 -1.637 0.981]
[5177.344] from 1
[-2.275 4.238 -1.637 0.981]
[ 4.172325e-08 -2.034375e+00] from 0
[-2.275 4.238 -1.637 0.981]
[2.264875] from 2
I cannot understand where the strange numbers come from. The result should be [-2.275 4.238] from 0, [-1.637] from 1, [0.981] from 2 if right.
Does anyone have an idea? Thank you very much.
————————————————————————————————————————————
Update:
I find if the numbers in np.array are float, it will have this problem. I try to change the DATATYPE to MPI.INT or MPI.F_FLOAT, but it still doesn't work.
It seems caused by random, but I need to randomly generate the position.
I really do not know how to correct it.
python numpy mpi4py
python numpy mpi4py
asked Nov 19 '18 at 14:36
RunningRunning
12
asked Nov 19 '18 at 14:36
RunningRunning
12
edited Nov 20 '18 at 6:39
Running
asked Nov 19 '18 at 14:36
RunningRunning
12
asked Nov 19 '18 at 14:36
RunningRunning
12
asked Nov 19 '18 at 14:36
RunningRunning
12
12
add a comment |
add a comment |
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