More DLF improvements

This release is not completely backwards compatible for the main modelling routines in empymod.model, but almost. Read below to see which functions are affected.

• Improved Hankel DLF [empymod#11].
  empymod.kernel.wavenumber always returns three kernels, PJ0, PJ1, and PJ0b. The first one is angle-independent, the latter two depend on the angle. Now, depending of what source-receiver configuration is chosen, some of these might be zero. If-statements were now included to avoid the calculation of the DLF, interpolation, and reshaping for 0-kernels, which improves speed for these cases.

• Unified DLF arguments [empymod#10].

  These changes are backwards compatible for all main modelling routines in empymod.model. However, they are not backwards compatible for the following routines:

  • empymod.model.fem (removed use_spline),
  • empymod.transform.fht (removed use_spline),
  • empymod.transform.hqwe (removed use_spline),
  • empymod.transform.quad (removed use_spline),
  • empymod.transform.dlf (lagged, splined => pts_per_dec),
  • empymod.utils.check_opt (no longer returns use_spline),
  • empymod.utils.check_hankel (changes in pts_per_dec), and
  • empymod.utils.check_time (changes in pts_per_dec).

  The function empymod.utils.spline_backwards_hankel can be used for backwards compatibility.

  Now the Hankel and Fourier DLF have the same behaviour for pts_per_dec:

  • pts_per_dec = 0: Standard DLF,
  • pts_per_dec < 0: Lagged Convolution DLF, and
  • pts_per_dec > 0: Splined DLF.

  There is one exception which is not backwards compatible: Before, if opt=None and htarg={pts_per_dec: != 0}, the pts_per_dec was not used for the FHT and the QWE. New, this will be used according to the above definitions.

• Bugfix in model.wavenumber for ab=36 (zeroes).