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Correct slope calculation in clearsky.detect_clearsky #1242

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Merged
merged 4 commits into from
Jun 25, 2021
Merged

Correct slope calculation in clearsky.detect_clearsky #1242

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e942e6c
correct slope calculation, add test with time interval 2 minutes
cwhanse Jun 4, 2021
2d9fd8a
remove unneeded test adjustment
cwhanse Jun 4, 2021
976052c
add note to whatsnew
cwhanse Jun 17, 2021
2b3fe70
avoid diff twice
cwhanse Jun 17, 2021
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3 changes: 3 additions & 0 deletions docs/sphinx/source/whatsnew/v0.9.0.rst
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Expand Up @@ -167,6 +167,9 @@ Bug fixes
calling :py:func:`~pvlib.pvsystem.calcparams_cec`. (:issue:`1215`, :pull:`1216`)
* Corrected methodology error in :py:func:`~pvlib.scaling.wvm`. Tracks with
fix in PVLib for MATLAB. (:issue:`1206`, :pull:`1213`)
* Corrected an error affecting :py:func:`~pvlib.clearsky.detect_clearsky`
when data time step is not one minute. Error was introduced in v0.8.1.
(:issue:`1241`, :pull:`1242`)

Testing
~~~~~~~
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11 changes: 6 additions & 5 deletions pvlib/clearsky.py
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Expand Up @@ -633,17 +633,18 @@ def _calc_stats(data, samples_per_window, sample_interval, H):
# shift to get forward difference, .diff() is backward difference instead
data_diff = data.diff().shift(-1)
data_slope = data_diff / sample_interval
data_slope_nstd = _slope_nstd_windowed(data, H, samples_per_window)
data_slope_nstd = _slope_nstd_windowed(data_slope.values[:-1], data, H,
samples_per_window, sample_interval)
data_slope_nstd = data_slope_nstd

return data_mean, data_max, data_slope_nstd, data_slope


def _slope_nstd_windowed(data, H, samples_per_window):
def _slope_nstd_windowed(slopes, data, H, samples_per_window, sample_interval):
with np.errstate(divide='ignore', invalid='ignore'):
raw = np.diff(data)
raw = raw[H[:-1, ]].std(ddof=1, axis=0) / data.values[H].mean(axis=0)
return _to_centered_series(raw, data.index, samples_per_window)
nstd = slopes[H[:-1, ]].std(ddof=1, axis=0) \
/ data.values[H].mean(axis=0)
return _to_centered_series(nstd, data.index, samples_per_window)


def _max_diff_windowed(data, H, samples_per_window):
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11 changes: 11 additions & 0 deletions pvlib/tests/test_clearsky.py
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Expand Up @@ -607,6 +607,17 @@ def test_detect_clearsky_window(detect_clearsky_data):
check_dtype=False, check_names=False)


def test_detect_clearsky_time_interval(detect_clearsky_data):
expected, cs = detect_clearsky_data
u = np.arange(0, len(cs), 2)
cs2 = cs.iloc[u]
expected2 = expected.iloc[u]
clear_samples = clearsky.detect_clearsky(
expected2['GHI'], cs2['ghi'], window_length=6)
assert_series_equal(expected2['Clear or not'], clear_samples,
check_dtype=False, check_names=False)


def test_detect_clearsky_arrays(detect_clearsky_data):
expected, cs = detect_clearsky_data
clear_samples = clearsky.detect_clearsky(
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