Function opensn::MakeTwoGridCollapsedInfo

Function Documentation

TwoGridCollapsedInfo opensn::MakeTwoGridCollapsedInfo(const MultiGroupXS &xs, EnergyCollapseScheme scheme, unsigned int first_group, unsigned int last_group, double time_absorption_scale = 0.0, bool adjoint = false)

Computes the two-grid collapsed diffusion data for a material over the groups [first_group, last_group] of the accelerated groupset.

The returned spectrum is indexed by global group and is zero outside that range.

time_absorption_scale is 1/(theta dt) for a time-dependent problem and 0 otherwise. The time absorption 1/(v theta dt) that the theta scheme adds to the total cross section is included in the collapse so that the diffusion operator matches the transport operator being accelerated.

The collapse uses the transposed transfer matrix when adjoint is true, as a problem in adjoint mode does, and the forward transfer matrix otherwise.