Developer Reference for Intel® oneAPI Math Kernel Library for C
DFTI_NUMBER_OF_TRANSFORMS
If you need to perform a large number of identical FFTs, you can do this in a single call to a DftiCompute* function with the value of the DFTI_NUMBER_OF_TRANSFORMS configuration parameter equal to the actual number of the transforms. The default value of this parameter is 1. You can set this parameter to a positive integer value of the MKL_LONG data type. When setting the number of transforms to a value greater than one, you also need to specify the distance between the input data sets and the distance between the output data sets using one of the DFTI_INPUT_DISTANCE and DFTI_OUTPUT_DISTANCE configuration parameters or both.
The data sets to be transformed must not have common elements; the DFTI_INPUT_DISTANCE and DFTI_OUTPUT_DISTANCE must be set explicitly to ensure that all data sets for each transform are independent .
All the sets of data must be located within the same memory block.
To better understand usage of the DFTI_NUMBER_OF_TRANSFORMS configuration parameter, see this example in your Intel® oneAPI Math Kernel Library (oneMKL) directory:
./examples/dftc/source/config_number_of_transforms.c