Hello Federico,
--> isreal(%i^2, %eps)
ans =
T
--> %i^2 == -1
ans =
T
Regards
Stefan
On 2022-04-07 05:24, Federico Miyara wrote:
Dear all,
Consider
M = 16
w = [ones(1,M/4),zeros(1,M/4)]
w = [w(1:M/2), 0, conj(w($:-1:2))]
v = ifft(w)
isreal(v)
The first 3 lines defines a real spectrum of a real signal, then the
real signal is recovered and finally it is checked whether it is real or
not.
What puzzles me is that the result is T (true). However, the definition
of the ifft() involves complex operations, so at some point the numbers
must be converted to a complex representation such as
1. + 0.i
so I would expect that the result included 0i so the result of the test
should be F. Where is this null imaginary component removed?
I don't say this is wrong, but it is perplexing if compared to much more
simple operations such as
sqrt(%i^4)
which yields 1. + 0.i, a complex representation of real scalar 1.
Maybe the fftw package is so refined to detect whether the result is
actually real and removes the useless 0.i components?
Regards,
Federico Miyara
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