# Solver Layer

This module of the VTS implements various radiative transport models or solvers that the user may use to solve his/her problem. Only a subset of the total available solvers may be active based on the specific source/detector configurations and/or tissue geometry/properties specified by the user. We have plans to implement analytic, deterministic, and stochastic solvers. Solvers already developed (but not necessarily implemented within the VTS) by core investigators of the Virtual Photonics Technology Initiative are as follows where the letter in [] denotes whether the solver implementation is Analytic, Deterministic, or Stochastic.

- Standard Diffusion Approximation (SDA/P
_{1}) [A] -
- Internal dosimetry and reflectance/transmission.
- Steady-state and time-domain solvers
- Spatial frequency- and temporal frequency-domain solvers.

- Higher-Order 'Diffusion' Solvers (P
_{N}/δ-P_{N}) [A] - Conventional Monte Carlo [S]
- Condensed History Monte Carlo [S]
- Electric-Field Monte Carlo [S]

The graphical representation and references for this layer are given below. We are in the process of developing solvers using Adaptive Monte Carlo methods and hope, through collaboration, to incorporate Finite-Difference Time-Domain Solvers of the Maxwell's Equations. A graphical representation of the Solver Layer is shown below: