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)

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.