8000 BUG : fix scaling issue with mlab.psd and odd NFFT by tacaswell · Pull Request #4326 · matplotlib/matplotlib · GitHub
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BUG : fix scaling issue with mlab.psd and odd NFFT #4326

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Merged
merged 2 commits into from
Apr 12, 2015
Merged

BUG : fix scaling issue with mlab.psd and odd NFFT #4326

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17bc283
BUG : fix scaling issue with mlab.psd and odd NFFT
tacaswell Apr 10, 2015
01d2e6c
TST : add test of odd NFFT single sided psd
tacaswell Apr 12, 2015
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10 changes: 9 additions & 1 deletion lib/matplotlib/mlab.py
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Original file line number Diff line number Diff line change
Expand Up @@ -782,7 +782,15 @@ def _spectral_helper(x, y=None, NFFT=None, Fs=None, detrend_func=None,
# Also include scaling factors for one-sided densities and dividing by
# the sampling frequency, if desired. Scale everything, except the DC
# component and the NFFT/2 component:
result[1:-1] *= scaling_factor

# if we have a even number of frequencies, don't scale NFFT/2
if not NFFT % 2:
slc = slice(1, -1, None)
# if we have an odd number, just don't scale DC
else:
slc = slice(1, None, None)

result[slc] *= scaling_factor

# MATLAB divides by the sampling frequency so that density function
# has units of dB/Hz and can be integrated by the plotted frequency
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13 changes: 11 additions & 2 deletions lib/matplotlib/tests/test_mlab.py
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Expand Up @@ -2960,8 +2960,17 @@ def test_evaluate_equal_dim_and_num_lt(self):
np.testing.assert_array_almost_equal(y, y_expected, 7)


#*****************************************************************
#*****************************************************************
def test_psd_onesided_norm():
u = np.array([0, 1, 2, 3, 1, 2, 1])
dt = 1.0
Su = np.abs(np.fft.fft(u) * dt)**2 / float(dt * u.size)
P, f = mlab.psd(u, NFFT=u.size, Fs=1/dt, window=mlab.window_none,
detrend=mlab.detrend_none, noverlap=0, pad_to=None,
scale_by_freq=None,
sides='onesided')
Su_1side = np.append([Su[0]], Su[1:4] + Su[4:][::-1])
assert_allclose(P, Su_1side, atol=1e-06)


if __name__ == '__main__':
import nose
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