python中mpi4py的所有基础使用案例详解

python中mpi4py的所有基础使用案例详解

python中mpi4py的基础使用

大多数 MPI 程序都可以使用命令 mpiexec 运行。在实践中,运行 Python 程序如下所示:

$ mpiexec -n 4 python script.py

案例1:测试comm.send 和comm.recv函数,代码如下

from mpi4py import MPI comm = MPI.COMM_WORLD rank = comm.Get_rank() if rank == 0:     data = {'a': 7, 'b': 3.14}     comm.send(data, dest=1, tag=11) elif rank == 1:     data = comm.recv(source=0, tag=11)

rank代表进程编号,其总数是mpiexec -n中的n的个数,最大的n受到电脑cpu内核数的限制
dest代表发送的目标,tag是一个标志位可以忽略,source为数据来源rank标志

案例2:具有非阻塞通讯的python对象

from mpi4py import MPI comm = MPI.COMM_WORLD rank = comm.Get_rank() if rank == 0:     data = {'a': 7, 'b': 3.14}     req = comm.isend(data, dest=1, tag=11)     req.wait() elif rank == 1:     req = comm.irecv(source=0, tag=11)     data = req.wait()

案例3: 快速发送实例

这里的Send和Recv都是大写,用于numpy数据的传输

from mpi4py import MPI import numpy comm = MPI.COMM_WORLD rank = comm.Get_rank() # passing MPI datatypes explicitly if rank == 0:     data = numpy.arange(1000, dtype='i')     comm.Send([data, MPI.INT], dest=1, tag=77) elif rank == 1:     data = numpy.empty(1000, dtype='i')     comm.Recv([data, MPI.INT], source=0, tag=77) # automatic MPI datatype discovery if rank == 0:     data = numpy.arange(100, dtype=numpy.float64)     comm.Send(data, dest=1, tag=13) elif rank == 1:     data = numpy.empty(100, dtype=numpy.float64)     comm.Recv(data, source=0, tag=13)

案例4:集体通讯,广播机制

广播机制就是将当前root=0端口下的所有信息发送到任何一个进程

from mpi4py import MPI comm = MPI.COMM_WORLD rank = comm.Get_rank() if rank == 0:     data = {'key1' : [7, 2.72, 2+3j],             'key2' : ( 'abc', 'xyz')} else:     data = None data = comm.bcast(data, root=0)

案例5:scatter,将root=0下的数据一次分发到各个rank下

from mpi4py import MPI comm = MPI.COMM_WORLD size = comm.Get_size() rank = comm.Get_rank() if rank == 0:     data = [(i+1)**2 for i in range(size)] else:     data = None data = comm.scatter(data, root=0) assert data == (rank+1)**2

案例6:gather,将所有rank下的数据收集到root下

from mpi4py import MPI comm = MPI.COMM_WORLD size = comm.Get_size() rank = comm.Get_rank() data = (rank+1)**2 data = comm.gather(data, root=0) if rank == 0:     for i in range(size):         assert data[i] == (i+1)**2 else:     assert data is None

案例7,numpy的广播机制

与之前一样都是大写

from mpi4py import MPI import numpy as np comm = MPI.COMM_WORLD rank = comm.Get_rank() if rank == 0:     data = np.arange(100, dtype='i') else:     data = np.empty(100, dtype='i') comm.Bcast(data, root=0) for i in range(100):     assert data[i] == i

案例8:numpy的Scatter机制

from mpi4py import MPI import numpy as np comm = MPI.COMM_WORLD size = comm.Get_size() rank = comm.Get_rank() sendbuf = None if rank == 0:     sendbuf = np.empty([size, 100], dtype='i')     sendbuf.T[:,:] = range(size) recvbuf = np.empty(100, dtype='i') comm.Scatter(sendbuf, recvbuf, root=0) assert np.allclose(recvbuf, rank)

案例9:numpy的Gather机制

from mpi4py import MPI import numpy as np comm = MPI.COMM_WORLD size = comm.Get_size() rank = comm.Get_rank() sendbuf = np.zeros(100, dtype='i') + rank recvbuf = None if rank == 0:     recvbuf = np.empty([size, 100], dtype='i') comm.Gather(sendbuf, recvbuf, root=0) if rank == 0:     for i in range(size):         assert np.allclose(recvbuf[i,:], i)

案例10 :allgather机制

allgather就是 scatter 加上广播机制。
rank0 = a
rank1 = b
rank2 = c
allgather后结果为
rank0 = a,b,c
rank1 = a,b,c
rank2 = a,b,c

from mpi4py import MPI import numpy def matvec(comm, A, x):     m = A.shape[0] # local rows     p = comm.Get_size()     xg = numpy.zeros(m*p, dtype='d')     comm.Allgather([x,  MPI.DOUBLE],                    [xg, MPI.DOUBLE])     y = numpy.dot(A, xg)     return y

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