SED term for a single band.
The SED slope (in flux units) in the middle of a band is computed either
as an "interpolated" or "extrapolated" computation. See Burke et al. 2018
Appendix A (https://ui.adsabs.harvard.edu/abs/2018AJ....155...41B).
For interpolation, with a secondary term::
F'_nu ~ constant * (primaryTerm + secondaryTerm) / 2.0
For interpolation, without a secondary term::
F'_nu ~ constant * primaryTerm
For extrapolation::
F'_nu ~ primaryTerm + constant * (((lambda_primaryBand - lambda_secondaryBand) /
(lambda_primaryBand - lambda_tertiaryBand)) *
(primaryTerm - secondaryTerm))
where primaryTerm and secondaryTerm are names from a `SedboundarytermDict`, and
primaryBand, secondaryBand, and tertiaryBand are band names.
To construct a Sedterm, use keyword arguments::
Sedterm(primaryTerm=primaryTermName, secondaryTerm=secondaryTermName,
extrapolated=False, constant=1.0)
or::
Sedterm(primaryTerm=primaryTermName, secondaryTerm=secondaryTermName,
extrapolated=True, constant=1.0, primaryBand=primaryBandName,
secondaryBand=secondaryBandName, tertiaryBand=tertiaryBandName)
This is a subclass of Config. This follows the form of
`lsst.pipe.tasks.Colorterm`.
Definition at line 71 of file sedterms.py.