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DOC: fix the swt/swt2 start_level coefficient ranges #863

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rgommers merged 1 commit into from
Aug 17, 2026
+7 −8
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DOC: fix the swt/swt2 start_level coefficient ranges #863

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15 changes: 7 additions & 8 deletions pywt/_swt.py
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Original file line number Diff line number Diff line change
Expand Up @@ -41,7 +41,10 @@ def swt(data, wavelet, level=None, start_level=0, axis=-1,
start_level : int, optional
The level at which the decomposition will begin (it allows one to
skip a given number of transform steps and compute
coefficients starting from start_level) (default: 0)
coefficients starting from start_level) (default: 0). The output
always contains exactly ``level`` sets of coefficients, corresponding
to decomposition levels ``start_level + 1`` through
``start_level + level``.
axis: int, optional
Axis over which to compute the SWT. If not given, the
last axis is used.
Expand All @@ -66,7 +69,7 @@ def swt(data, wavelet, level=None, start_level=0, axis=-1,
If ``start_level = m`` is given, then the beginning m steps are
skipped::

[(cAm+n, cDm+n), ..., (cAm+1, cDm+1), (cAm, cDm)]
[(cAm+n, cDm+n), ..., (cAm+1, cDm+1)]

If ``trim_approx`` is ``True``, then the output list is exactly as in
``pywt.wavedec``, where the first coefficient in the list is the
Expand Down Expand Up @@ -165,7 +168,7 @@ def iswt(coeffs, wavelet, norm=False, axis=-1):
[(cAn, cDn), ..., (cA2, cD2), (cA1, cD1)]

where cA is approximation, cD is details. Index 1 corresponds to
``start_level`` from ``pywt.swt``.
``start_level + 1`` from ``pywt.swt``.
wavelet : Wavelet object or name string
Wavelet to use
norm : bool, optional
Expand Down Expand Up @@ -309,9 +312,6 @@ def swt2(data, wavelet, level, start_level=0, axes=(-2, -1),
...,
(cA_m+1,
(cH_m+1, cV_m+1, cD_m+1)
),
(cA_m,
(cH_m, cV_m, cD_m)
)
]

Expand All @@ -327,7 +327,6 @@ def swt2(data, wavelet, level, start_level=0, axes=(-2, -1),
(cH_m+level, cV_m+level, cD_m+level),
...,
(cH_m+1, cV_m+1, cD_m+1),
(cH_m, cV_m, cD_m),
]

Notes
Expand Down Expand Up @@ -402,7 +401,7 @@ def iswt2(coeffs, wavelet, norm=False, axes=(-2, -1)):

where cA is approximation, cH is horizontal details, cV is
vertical details, cD is diagonal details and n is the number of
levels. Index 1 corresponds to ``start_level`` from ``pywt.swt2``.
levels. Index 1 corresponds to ``start_level + 1`` from ``pywt.swt2``.
wavelet : Wavelet object or name string, or 2-tuple of wavelets
Wavelet to use. This can also be a 2-tuple of wavelets to apply per
axis.
Expand Down