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# SHTOOLS/SHTOOLS: Version 4.9.1

markwieczorek; Matthias Meschede; Ilya Oshchepkov; Elliott Sales de Andrade; mreineck; Armin Corbin; xoviat; Benda Xu; Stefan Schröder; Akihisa Hattori; Aaryaman Vasishta; Andrew Walker; Erik Schnetter; Katrin Leinweber

Version 4.9

Backends

Implemented the option to use a different backend when performing certain operations requiring spherical harmonic transforms. At present, only 'shtools' (default) and the Distinctly Useful Code Collection ('ducc') are supported.

• Introduced a new module backends that has functions allowing the user to control which backend is used. To set the backend for all subsequent operations, use backends.select_preferred_backend().
• Added the optional parameters backend and nthreads ('ducc' only) to all methods of the pyshtools classes that allow multiple backends (such as SHGrid and SHCoeffs).
• Added a new backends web documentation page that describes the use of the new module.

Plotting routines

• Added the new methods SHGrid.histogram() and SHGrid.plot_histogram() for generating area-weighted histograms.
• Renamed a few instances of variable names used in the plotting routines from title_labelsize to titlesize for consistency. This affects the methods Slepian.plot_coupling_matrix(), Slepian.plot_spectra(), and SHWindow.plot_coupling_matrix().
• Modified some plotting routines so that fontsizes can be specified using standard matplotlib strings.
• Replaced the deprecated matplotlib get_geometry with get_subplotspec.
• Replaced the pygmt option I with the alias shading for colorbars.

IO and datasets

• Updated the Venus rotation period using data from Margot et al. (2021).
• Renamed constants variables r to mean_radius (but kept r as an alias for backwards compatibility).
• Improved the reading of ICGEM formatted files of gravitational potential models. Fixed a bug where the time variable contribution was not computed when the coefficients had an associated trnd or dot term. When a line in the data section starts with an unknown key, a warning is now printed to the screen (which can be turned off by specifying quiet=True). For files formatted as icgem2.0, time variable terms were simply ignored if the specified epoch fell outside of the allowed range. Now, the routine will instead raise an error. Finally, the documentation was improved by describing the allowable keyword entries of the header and data section of the file.
• Added the option encoding for all routines and methods that read or write text-based spherical harmonic files.
• Hard coded all datasets to use utf-8 in order to avoid problems with the XGM2019E dataset that has a character that can not be decoded by the GBK encoding that is the default in some Chinese installations.
• Added a few historical lunar gravity fields to the module datasets.Moon.historical.gravity.

Other changes

• Added a C wrapper for the function MakeGradientDH().
• Changed the default behavior of the Fortran routine MakeGradientDH() and SHCoeffs.gradient(). The original behavior was to compute the gradient on a sphere of radius r, where r was the degree 0 coefficient of the function. The new behaviour is to compute the gradient on the unit sphere. This radius can be modified by supplying the optional argument radius.
• Added the option 'per_lm' for generating random spherical harmonic coefficients in the .from_random() methods of SHCoeffs, SHGravCoeffs, and SHMagCoeffs.
• Fixed two bugs related to complex spherical harmonic transforms. First, for complex grids, the last coefficient coeffs[1, lmax, lmax] was in error when lmax was odd and when using DH grids. Second, when using SHGrid.expand() with grid type DH2 the parameter sampling=2 was not passed to the Fortran routine.
• Updated makefile install to include example data files, and to place them in the correct directories when installing with homebrew.
• Updated a few dependencies, including astropy>=4.0 and pygmt>=0.3.0.
• Fixed a floating point error-caused bug in SHGrid that could arise if the value input to arccos was greater than 1.
• Converted np.float_ and np.complex_ to np.float64 and np.complex128 to avoid numpy deprectation warning.
• Added threadsafe to numpy signature files.

M. A. Wieczorek, M. Meschede, T. Brugere, A. Corbin, A. Hattori, K. Leinweber, I. Oshchepkov, M. Reinecke, E. Sales de Andrade, E. Schnetter, S. Schröder, A. Vasishta, A. Walker, B. Xu (2021). SHTOOLS: Version 4.9, Zenodo, doi:10.5281/zenodo.592762

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