A Python module for continuous wavelet spectral analysis. It includes a collection of routines for wavelet transform and statistical analysis via FFT algorithm. In addition, the module also includes cross-wavelet transforms, wavelet coherence tests and sample scripts.
Please read the documentation on http://regeirk.github.io/pycwt/.
This module requires NumPy and SciPy. In addition, you also need
matplotlib to run the samples.
The sample scripts (sample.py, sample_xwt.py) illustrate the use of
the wavelet and inverse wavelet transforms, cross-wavelet transform and
wavelet transform coherence. Results are plotted in figures similar to the
sample images.
This module is based on routines provided by C. Torrence and G. P. Compo available at http://paos.colorado.edu/research/wavelets/, on routines provided by A. Grinsted, J. Moore and S. Jevrejeva available at http://noc.ac.uk/using-science/crosswavelet-wavelet-coherence, and on routines provided by A. Brazhe available at http://cell.biophys.msu.ru/static/swan/.
This software is released under a BSD-style open source license. Please read the license file for further information. This routine is provided as is without any express or implied warranties whatsoever.
You can use PyPI to install this package.
>> pip install pycwt
Or, you can download the code and run the below line within the top level folder.
>> python setup.py install
There is an errata page at the wavelet website maintained at the Program in Atmospheric and Oceanic Sciences, University of Colorado, Boulder, Colorado, which is accessible at http://paos.colorado.edu/research/wavelets/errata.html
Christopher Torrence and Gilbert P. Compo
Program in Atmospheric and Oceanic Sciences, University of Colorado, Boulder, Colorado
- Figure 3: N/(2 sigma^2) should just be N/sigma^2.
- Equation (17), left-hand side: Factor of 1/2 should be removed.
- Table 1, DOG, Psi-hat (third column, bottom row): Should be a minus sign in front of the equation.
- Sec 3f, last paragraph: Plugging N=506, dt=1/4 yr, s0=2dt, and dj=0.125 into Eqn (10) actually gives J=64, not J=56 as stated in the text. However, in Figure 1b, the scales are only plotted out to J=56 since the power is so low at larger scales.
Table 3: Cross-wavelet significance levels, from Eqn.(30)-(31). (DOF = degrees of freedom)
Significance level Real wavelet (1 DOF) Complex wavelet (2 DOF) 0.10 | 1.595 | 3.214 0.05 | 2.182 | 3.999 0.01 | 3.604 | 5.767
We would like to thank Christopher Torrence, Gilbert P. Compo, Aslak Grinsted, John Moore, Svetlana Jevrejevaand and Alexey Brazhe for their code and also Jack Ireland and Renaud Dussurget for their attentive eyes, feedback and debugging.
Sebastian Krieger, Nabil Freij, Alexey Brazhe, Christopher Torrence, Gilbert P. Compo and contributors.
- Torrence, C. and Compo, G. P.. A Practical Guide to Wavelet Analysis. Bulletin of the American Meteorological Society, American Meteorological Society, 1998, 79, 61-78. http://dx.doi.org/10.1175/1520-0477(1998)079\<0061:APGTWA>2.0.CO;2>
- Torrence, C. and Webster, P. J.. Interdecadal changes in the ENSO-Monsoon system, Journal of Climate, 1999, 12(8), 2679-2690. http://dx.doi.org/10.1175/1520-0442(1999)012\<2679:ICITEM>2.0.CO;2>
- Grinsted, A.; Moore, J. C. & Jevrejeva, S. Application of the cross wavelet transform and wavelet coherence to geophysical time series. Nonlinear Processes in Geophysics, 2004, 11, 561-566. http://dx.doi.org/10.5194/npg-11-561-2004
- Mallat, S.. A wavelet tour of signal processing: The sparse way. Academic Press, 2008, 805.
- Addison, P. S. The illustrated wavelet transform handbook: introductory theory and applications in science, engineering, medicine and finance. IOP Publishing, 2002. http://dx.doi.org/10.1201/9781420033397
- Liu, Y., Liang, X. S. and Weisberg, R. H. Rectification of the bias in the wavelet power spectrum. Journal of Atmospheric and Oceanic Technology, 2007, 24, 2093-2102. http://dx.doi.org/10.1175/2007JTECHO511.1