pyopensn.solver.NonLinearKEigenSolver

class pyopensn.solver.NonLinearKEigenSolver

Non-linear k-eigenvalue solver.

Wrapper of opensn::NonLinearKEigenSolver.

Supports one or more groupsets when the groupsets run without WGDSA/TGDSA. If WGDSA or TGDSA is enabled on any groupset, the nonlinear k-eigen solve must use a single groupset; otherwise Initialize() raises a ValueError.

The eigenvector is returned with an arbitrary scale that depends on the solver, the acceleration method, and the starting flux. Normalize absolute quantities (power, reaction rates, leakage, balance rates) explicitly, e.g. with power_normalization_target.

Advance(self: pyopensn.solver.Solver) → None

Advance the solver by one step.

Changes made to the problem since the last step are checked as in Execute. Initialize must be called first. Solver classes that do not implement stepping leave the state unchanged and log that Advance is unsupported.

For MPI transport solvers, this is a collective operation and must be called on all ranks.

ComputeBalanceTable(self: pyopensn.solver.NonLinearKEigenSolver) → dict

Compute and return the global balance table using the solver’s normalization. This is a collective operation and must be called on all ranks.

Returns:

Dictionary with the following entries:

  • absorption_rate: Global absorption rate, approximately integral sigma_a * phi dV summed over groups and the full domain.

  • production_rate: Global volumetric production/source rate used by the solver, approximately integral Q dV summed over groups and the full domain.

  • inflow_rate: Global incoming boundary contribution integrated over incoming angular flux on boundaries. On reflecting boundaries the outgoing partial current is counted as the incoming one, so reflecting faces add equal amounts to inflow_rate and outflow_rate and cancel in balance.

  • outflow_rate: Global outgoing boundary contribution accumulated from face outflow tallies, including reflecting boundaries (see inflow_rate).

  • balance: Rate balance, production_rate + inflow_rate - absorption_rate - outflow_rate.

Return type:

dict

Notes

For k-eigenvalue balance reporting, this solver scales the production term by 1 / k_eff before forming both production_rate and balance.

Execute(self: pyopensn.solver.Solver) → None

Execute the solver.

The problem’s current state and the solver’s requirements are checked first, so changes made to the problem after Initialize (for example a mode switch or SetXSMap) are validated before they are used. Initialize must be called before Execute.

For MPI transport solvers, this is a collective operation and must be called on all ranks.

GetEigenvalue(self: pyopensn.solver.NonLinearKEigenSolver) → float

Return the current k-eigenvalue.

GetNumSweeps(self: pyopensn.solver.NonLinearKEigenSolver) → int

Return the cumulative number of transport sweeps performed by all groupsets, including those of the initial power iterations.

Returns:

Total number of transport sweeps.

Return type:

int

Initialize(self: pyopensn.solver.Solver) → None

Initialize the solver.

Solvers check that the problem is in a supported state (for example, steady-state mode without external sources for the k-eigenvalue solvers) and raise ValueError otherwise. Setup and post-setup validation must both succeed. Calling Initialize again clears the previous initialized state first.

For MPI transport solvers, this is a collective operation and must be called on all ranks.

IsConverged(self: pyopensn.solver.NonLinearKEigenSolver) → bool

Return True if the nonlinear solve of the last Execute() converged.

Returns False if the nonlinear solver stopped on its iteration limit or another divergence reason, and before the first Execute().

__init__(self: pyopensn.solver.NonLinearKEigenSolver, **kwargs) → None

Construct a non-linear k-eigenvalue solver.

Parameters:

  • problem (pyopensn.solver.DiscreteOrdinatesProblem) – Existing discrete ordinates problem instance. Multiple groupsets are supported when groupset WGDSA/TGDSA is disabled. If WGDSA or TGDSA is enabled on any groupset, the nonlinear k-eigen solve must use a single groupset.

  • nl_abs_tol (float, default=1.0e-8) – Non-linear absolute tolerance.

  • nl_rel_tol (float, default=1.0e-8) – Non-linear relative tolerance.

  • nl_sol_tol (float, default=1.0e-50) – Non-linear solution tolerance.

  • nl_max_its (int, default=50) – Non-linear algorithm maximum iterations.

  • l_abs_tol (float, default=1.0e-8) – Linear absolute tolerance. The value used is min(l_abs_tol, nl_abs_tol), so that the linear solves can reduce the nonlinear residual below nl_abs_tol.

  • l_rel_tol (float, default=1.0e-8) – Linear relative tolerance.

  • l_div_tol (float, default=1.0e6) – Linear divergence tolerance.

  • l_max_its (int, default=50) – Linear algorithm maximum iterations.

  • l_gmres_restart_intvl (int, default=30) – GMRES restart interval.

  • l_gmres_breakdown_tol (float, default=0.1) – GMRES breakdown tolerance.

  • reset_phi0 (bool, default=True) – If true, reinitializes scalar fluxes to 1.0.

  • num_initial_power_iterations (int, default=0) – Number of initial power iterations before the non-linear solve.

  • compute_balance (bool, default=False) – If true, print the balance table, with production scaled by 1/k_eff, after Execute() completes.

Notes

PETSc convergence failures and iteration limits are reported through the solver status and log output, consistent with the other transport solvers. Invalid residual states are reported to PETSc as function-domain errors so SNES can backtrack or terminate with the appropriate reason.