abec is the abbreviation for the form of the linear system we solve.
See, e.g,  https://github.com/BoxLib-Codes/BoxLib/blob/master/Src/LinearSolvers/C_CellMG/ABecLaplacian.H


The dcf routines are the D coefficient in Eq. 46 of the gray radiation paper

A lot of the routines have two variants, with the alternate having "3"
at the end of the name (like hbmat and hbmat3).  The ones with "3" are
the physical boundary variants.

