Developer Reference

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DftiComputeBackwardDM

Computes the backward FFT.

Syntax

status
=
DftiComputeBackwardDM
(
handle
,
in_X
,
out_X
)
;
status
=
DftiComputeBackwardDM
(
handle
,
in_out_X
)
;
Include Files
  • mkl_cdft.h
Input Parameters
handle
The descriptor handle.
in_X, in_out_X
Local part of input data. Array of complex values. Refer to Distributing Data among Processes on how to allocate and initialize the array.
Output Parameters
out_X, in_out_X
Local part of output data. Array of complex values. Refer to Distributing Data among Processes on how to allocate the array.
Description
The
DftiComputeBackwardDM
function computes the backward FFT.
Backward FFT is the transform using the factor
e
i2π/n
.
Before you call the function, the valid descriptor, created by
DftiCreateDescriptorDM
, must be configured and committed using the
DftiCommitDescriptorDM
function.
The computation is carried out by calling the
DftiComputeBackward
function. So, the functions have very much in common, and details not explicitly mentioned below can be found in the description of
DftiComputeBackward
.
Local part of input data, as well as local part of the output data, is an appropriate sequence of complex values (each complex value consists of two real numbers: real part and imaginary part) that a particular process stores. See Distributing Data among Processes for details.
Refer to Configuration Settings for the list of configuration parameters that the descriptor passes to the function.
The configuration parameter
DFTI_PRECISION
determines the precision of input data, output data, and transform: a setting of
DFTI_SINGLE
indicates single-precision floating-point data type and a setting of
DFTI_DOUBLE
indicates double-precision floating-point data type.
The configuration parameter
DFTI_PLACEMENT
informs the function whether the computation should be in-place. If the value of this parameter is
DFTI_INPLACE
(default), you must call the function with two parameters, otherwise you must supply three parameters. If
DFTI_PLACEMENT = DFTI_INPLACE
and three parameters are supplied, then the third parameter is ignored.
Even in case of an out-of-place transform, local array of input data
in_X
may be changed. To save data, make its copy before calling
DftiComputeBackwardDM
.
In case of an in-place transform,
DftiComputeBackwardDM
dynamically allocates and deallocates a work buffer of the same size as the local input/output array requires.
You can specify your own workspace of the same size through the configuration parameter
CDFT_WORKSPACE
to avoid redundant memory allocation.
Return Values
The function returns
DFTI_NO_ERROR
when completes successfully. If the function fails, it returns a value of another error class constant (for the list of constants, refer to Error Codes).
Prototype
    MKL_LONG DftiComputeBackwardDM(DFTI_DESCRIPTOR_DM_HANDLE handle, void *in_X,...);    

Product and Performance Information

1

Intel's compilers may or may not optimize to the same degree for non-Intel microprocessors for optimizations that are not unique to Intel microprocessors. These optimizations include SSE2, SSE3, and SSSE3 instruction sets and other optimizations. Intel does not guarantee the availability, functionality, or effectiveness of any optimization on microprocessors not manufactured by Intel. Microprocessor-dependent optimizations in this product are intended for use with Intel microprocessors. Certain optimizations not specific to Intel microarchitecture are reserved for Intel microprocessors. Please refer to the applicable product User and Reference Guides for more information regarding the specific instruction sets covered by this notice.

Notice revision #20110804