I have used complex FFT In my program, at first I usedFFTCF and FFTBFof IMSL, the computing resultwas correct. And for some reason, I had to replace the FFTCF and FFTBFwith CFFT1Dof MKL, but the problem come into being, the computing result is incorrect, the MKL fft transform resultwas muchsmaller than IMSL FFT, why? Thank you!

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Youcansubmit this problem into Intel premeir support website with your test code. MKL support engineer can work withyou for this problem.



Chao's recommendation is good and proper, but because of part of the nature of what you have done, I want to respond in the forum to this. Based on the information you provided I cannot answer why you got the results you did and why they differ from those you get with IMSL.

However, I can say that you are using the wrong functions. FFT functions such as CFFT1D is old code and we recommend against using it in MKL. You should be using the functions which are described in Chaper 11 of MKLMAN for MKL 8.0, titled "Fourier Transform Functions".

There have been no developments on the function you are using for several years and we indicate that these functions have been deprecated. While they are easy to use, they also lack much of the functionality the newer routines have.

We are seriously considering dropping them entirely from the library but providing a path to the use of the FFTs through some example code that the user could compile and link along with MKL to give access to the newer functions through the old interface. Of course users could then also look at that code and see how to use the newer functions and make the changes to their programs negating the need for the interface.

Getting back to your original question, I would look very carefully the parameters. Are you setting isign correctly? Is it in the right position? The fact the output is so short suggests that perhaps isign is in the size parameter location.


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