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Any one uses ESSL FFT package?

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Old   February 10, 2013, 14:38
Default Any one uses ESSL FFT package?
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Hi

I have to read a code, in which it would call IBM's ESSL FFT functions, like DRCFT and DCRFT. Since I will run it on my laptop where I hope to do the fft with fftpack, so I have to rewrite the DRCFT etc.

Now one of my questions is
after calling DRCFT, how the outcome array is stored?

For example, I call the forward fourier transform
CALL DRCFT (init, x, inc2x, x, inc2y, n, m, 1, scale=1, aux1, naux1, aux2, naux2)

x is the would-to-be-ffted array (real), and the outcome, which should be a complex array, however, would still be stored in x.

Then if, for example, the input is
x=[1 0.707 0 -0.707 -1 -0.707 0 0.707]
What should be outcome x be? I know in the outcome x(1)=0 (which is the sum, since the scale is 1), but what is x(2)?

In Matlab, x(2) of the outcome should be the real part of the second mode, but I suspect in ESSL FFT, the x(2) is the imaginary part of the first mode?

Sorry for the text not being clear.
Thanks in advance for any comments.
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