Chris@19: Next: MPI Plan Creation, Chris@19: Previous: Using MPI Plans, Chris@19: Up: FFTW MPI Reference Chris@19:
As described above (see MPI Data Distribution), in order to
Chris@19: allocate your arrays, before creating a plan, you must first
Chris@19: call one of the following routines to determine the required
Chris@19: allocation size and the portion of the array locally stored on a given
Chris@19: process. The MPI_Comm communicator passed here must be
Chris@19: equivalent to the communicator used below for plan creation.
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The basic interface for multidimensional transforms consists of the Chris@19: functions: Chris@19: Chris@19:
ptrdiff_t fftw_mpi_local_size_2d(ptrdiff_t n0, ptrdiff_t n1, MPI_Comm comm, Chris@19: ptrdiff_t *local_n0, ptrdiff_t *local_0_start); Chris@19: ptrdiff_t fftw_mpi_local_size_3d(ptrdiff_t n0, ptrdiff_t n1, ptrdiff_t n2, Chris@19: MPI_Comm comm, Chris@19: ptrdiff_t *local_n0, ptrdiff_t *local_0_start); Chris@19: ptrdiff_t fftw_mpi_local_size(int rnk, const ptrdiff_t *n, MPI_Comm comm, Chris@19: ptrdiff_t *local_n0, ptrdiff_t *local_0_start); Chris@19: Chris@19: ptrdiff_t fftw_mpi_local_size_2d_transposed(ptrdiff_t n0, ptrdiff_t n1, MPI_Comm comm, Chris@19: ptrdiff_t *local_n0, ptrdiff_t *local_0_start, Chris@19: ptrdiff_t *local_n1, ptrdiff_t *local_1_start); Chris@19: ptrdiff_t fftw_mpi_local_size_3d_transposed(ptrdiff_t n0, ptrdiff_t n1, ptrdiff_t n2, Chris@19: MPI_Comm comm, Chris@19: ptrdiff_t *local_n0, ptrdiff_t *local_0_start, Chris@19: ptrdiff_t *local_n1, ptrdiff_t *local_1_start); Chris@19: ptrdiff_t fftw_mpi_local_size_transposed(int rnk, const ptrdiff_t *n, MPI_Comm comm, Chris@19: ptrdiff_t *local_n0, ptrdiff_t *local_0_start, Chris@19: ptrdiff_t *local_n1, ptrdiff_t *local_1_start); Chris@19:Chris@19:
These functions return the number of elements to allocate (complex
Chris@19: numbers for DFT/r2c/c2r plans, real numbers for r2r plans), whereas
Chris@19: the local_n0 and local_0_start return the portion
Chris@19: (local_0_start to local_0_start + local_n0 - 1) of the
Chris@19: first dimension of an n0 × n1 × n2 × … × nd-1 array that is stored on the local
Chris@19: process. See Basic and advanced distribution interfaces. For
Chris@19: FFTW_MPI_TRANSPOSED_OUT plans, the ‘_transposed’ variants
Chris@19: are useful in order to also return the local portion of the first
Chris@19: dimension in the n1 × n0 × n2 ×…× nd-1 transposed output.
Chris@19: See Transposed distributions.
Chris@19: The advanced interface for multidimensional transforms is:
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ptrdiff_t fftw_mpi_local_size_many(int rnk, const ptrdiff_t *n, ptrdiff_t howmany, Chris@19: ptrdiff_t block0, MPI_Comm comm, Chris@19: ptrdiff_t *local_n0, ptrdiff_t *local_0_start); Chris@19: ptrdiff_t fftw_mpi_local_size_many_transposed(int rnk, const ptrdiff_t *n, ptrdiff_t howmany, Chris@19: ptrdiff_t block0, ptrdiff_t block1, MPI_Comm comm, Chris@19: ptrdiff_t *local_n0, ptrdiff_t *local_0_start, Chris@19: ptrdiff_t *local_n1, ptrdiff_t *local_1_start); Chris@19:Chris@19:
These differ from the basic interface in only two ways. First, they
Chris@19: allow you to specify block sizes block0 and block1 (the
Chris@19: latter for the transposed output); you can pass
Chris@19: FFTW_MPI_DEFAULT_BLOCK to use FFTW's default block size as in
Chris@19: the basic interface. Second, you can pass a howmany parameter,
Chris@19: corresponding to the advanced planning interface below: this is for
Chris@19: transforms of contiguous howmany-tuples of numbers
Chris@19: (howmany = 1 in the basic interface).
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The corresponding basic and advanced routines for one-dimensional Chris@19: transforms (currently only complex DFTs) are: Chris@19: Chris@19:
ptrdiff_t fftw_mpi_local_size_1d( Chris@19: ptrdiff_t n0, MPI_Comm comm, int sign, unsigned flags, Chris@19: ptrdiff_t *local_ni, ptrdiff_t *local_i_start, Chris@19: ptrdiff_t *local_no, ptrdiff_t *local_o_start); Chris@19: ptrdiff_t fftw_mpi_local_size_many_1d( Chris@19: ptrdiff_t n0, ptrdiff_t howmany, Chris@19: MPI_Comm comm, int sign, unsigned flags, Chris@19: ptrdiff_t *local_ni, ptrdiff_t *local_i_start, Chris@19: ptrdiff_t *local_no, ptrdiff_t *local_o_start); Chris@19:Chris@19:
As above, the return value is the number of elements to allocate
Chris@19: (complex numbers, for complex DFTs). The local_ni and
Chris@19: local_i_start arguments return the portion
Chris@19: (local_i_start to local_i_start + local_ni - 1) of the
Chris@19: 1d array that is stored on this process for the transform
Chris@19: input, and local_no and local_o_start are the
Chris@19: corresponding quantities for the input. The sign
Chris@19: (FFTW_FORWARD or FFTW_BACKWARD) and flags must
Chris@19: match the arguments passed when creating a plan. Although the inputs
Chris@19: and outputs have different data distributions in general, it is
Chris@19: guaranteed that the output data distribution of an
Chris@19: FFTW_FORWARD plan will match the input data distribution
Chris@19: of an FFTW_BACKWARD plan and vice versa; similarly for the
Chris@19: FFTW_MPI_SCRAMBLED_OUT and FFTW_MPI_SCRAMBLED_IN flags.
Chris@19: See One-dimensional distributions.
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