DftiComputeBackward

Developer Reference for Intel® oneAPI Math Kernel Library for C

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ID 766684

Date 3/31/2023

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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_inout, 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.	Data to be transformed in case of a real forward domain or, in the case of a complex forward domain in association with DFTI_COMPLEX_COMPLEX, set for DFTI_COMPLEX_STORAGE.
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 forward domain in association with DFTI_REAL_REAL set for DFTI_COMPLEX_STORAGE.

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 or, in the case of a complex forward domain in association with DFTI_COMPLEX_COMPLEX, set for DFTI_COMPLEX_STORAGE.
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 in association with DFTI_REAL_REAL set for DFTI_COMPLEX_STORAGE.
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 forward domain and the precision of the transform are determined by the configuration settings DFTI_FORWARD_DOMAIN and DFTI_PRECISION, which are during construction of the descriptor.

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 *, ... );

Parent topic: FFT Computation Functions

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DftiComputeBackward

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