Which matrix will dctimestep read from BSDF file when conducting matrix multiplication

BSDF file usually includes multiple matrices, such as Front BTDF, Back BTDF, Front BRDF and Back BRDF. When conducting three-phase simulation, which matrix will be used by default? Is there any options allow users to specify it?

By default, I believe the inside → outside matrix (or “Back Transmission” in WINDOW parlance) is used by dctimestep if present. Otherwise, the “Front Transmission” (outside → inside) matrix is transposed and applied. You cannot choose except by editing the XML file. However, the rmtxop command includes an option to specify the desired matrix, and can perform some of the same tasks as dctimestep, albeit less efficiently.


P.S. I just checked, and the rmtxop behavior is the same as dcmatrix regarding which transmission matrix is applied, though it does offer options for choosing reflectance matrices, instead.