Developer Reference

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DftiComputeBackward

Computes the backward FFT.

Syntax

status
=
DftiComputeBackward
(
desc_handle
,
x_inout
)
;
status
=
DftiComputeBackward
(
desc_handle
,
y_in
,
x_out
)
;
status
=
DftiComputeBackward
(
desc_handle
,
xre_in
out,
xim_inout
)
;
status
=
DftiComputeBackward
(
desc_handle
,
yre_in
,
yim_in
,
xre_out
,
xim_out
)
;
Input Parameters
Name
Type
Description
desc_handle
DFTI_DESCRIPTOR_HANDLE
FFT descriptor.
x_inout, y_in
Array of type
float
or
double
depending on the precision of the transform, specified in the
DFTI_PRECISION
configuration setting.
Data to be transformed in case of a real backward domain, determined by the
DFTI_FORWARD_DOMAIN
configuration setting.
xre_inout, xim_inout, yre_in, yim_in
Array of type
float
or
double
depending on the precision of the transform.
Real and imaginary parts of the data to be transformed in the case of a complex backward domain, determined by the
DFTI_FORWARD_DOMAIN
configuration setting.
The suffix in parameter names corresponds to the value of the configuration parameter
DFTI_PLACEMENT
as follows:
  • _inout
    to
    DFTI_INPLACE
  • _in
    to
    DFTI_NOT_INPLACE
Output Parameters
Name
Type
Description
x_out
Array of type
float
or
double
depending on the precision of the transform.
The transformed data in case of a real forward domain, specified in the
DFTI_FORWARD_DOMAIN
configuration setting.
xre_inout, xim_inout, xre_out, xim_out
Array of type
float
or
double
depending on the precision of the transform.
Real and imaginary parts of the transformed data in the case of a complex forward domain, specified in the
DFTI_FORWARD_DOMAIN
configuration setting.
status
MKL_LONG
Function completion status.
The suffix in parameter names corresponds to the value of the configuration parameter
DFTI_PLACEMENT
as follows:
  • _inout
    to
    DFTI_INPLACE
  • _out
    to
    DFTI_NOT_INPLACE
Include Files
  • mkl.h
Description
The function accepts the descriptor handle parameter and one or more data parameters. Given a successfully configured and committed descriptor,
the DftiComputeBackward
function computes the
inverse
FFT, that is, the transform with the
plus
sign in the exponent,
δ
= +1
.
The
DFTI_COMPLEX_STORAGE, DFTI_REAL_STORAGE
, and
DFTI_CONJUGATE_EVEN_STORAGE
configuration parameters define the layout of the input and output data and must be properly set in a call to the DftiSetValue function.
The FFT descriptor must be properly configured prior to the function call. Function calls needed to configure an FFT descriptor for a particular call to an FFT computation function are summarized in Configuring and Computing an FFT in C C++.
The number and types of the data parameters that the function requires may vary depending on the configuration of the descriptor. This variation is accommodated by
variable parameters
.
The function returns zero when it completes successfully.
See Status Checking Functions for more information on the returned status.
Prototype
     MKL_LONG DftiComputeBackward( DFTI_DESCRIPTOR_HANDLE, void *, ... );  

Product and Performance Information

1

Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.