[SciPy-dev] numpy.dft.real_fft problems?
Andrew Jaffe
a.h.jaffe at gmail.com
Fri Jan 13 08:00:16 CST 2006
Hi All,
[My apologies if this appears twice -- originally sent from a
non-subscribed account; moderator, please delete the original if possible!]
There seems to be a problem with the real_fft routine; starting with a
length n array, it should give a length n/2+1 array with real numbers
in the first and last positions (for n even). For a 2d array starting
with an (n,n) array, it should give a (n,n/2+1) array with real numbers
in the first and last positions on the first row. However, note that the
last entry on the first row has a real part, as opposed to the 2d
complex routine fft2d, which has it correct.
The weirdness of the real part seems to imply it's due to uninitialized
memory.
The problem persists in 2d, as well.
In [53]:a = numpy.randn(16)
In [54]:fa = numpy.dft.real_fft(a)
In [55]:fa
Out[55]:
array([ 0.4453+0.0000e+000j, -3.5009-3.4618e+000j, -0.1276+3.5740e-001j,
-1.043+2.3504e+000j, -1.2028+1.6121e-001j, -7.1041-1.1182e+000j,
0.09-1.6013e-001j, 4.2079-1.0106e-001j, -4.8295+2.3091e+251j])
In [56]:f2a = numpy.dft.fft(a)
In [57]:f2a
Out[57]:
array([ 0.4453+0.j , -3.5009-3.4618j, -0.1276+0.3574j,
-1.043+2.3504j, -1.2028+0.1612j, -7.1041-1.1182j, 0.09-0.1601j,
4.2079-0.1011j, -4.8295+0.j ,
4.2079+0.1011j,
0.09+0.1601j, -7.1041+1.1182j, -1.2028-0.1612j, -1.043-2.3504j,
-0.1276-0.3574j, -3.5009+3.4618j])
-Andrew
More information about the Scipy-dev
mailing list