Source code for openmdao.solvers.nonlinear.nonlinear_block_gs

"""Define the NonlinearBlockGS class."""

import numpy as np

from openmdao.solvers.solver import NonlinearSolver
from openmdao.utils.mpi import MPI

[docs]class NonlinearBlockGS(NonlinearSolver): """ Nonlinear block Gauss-Seidel solver. Parameters ---------- **kwargs : dict Options dictionary. Attributes ---------- _delta_outputs_n_1 : ndarray Cached change in the full output vector for the previous iteration. Only used if the aitken acceleration option is turned on. _theta_n_1 : float Cached relaxation factor from previous iteration. Only used if the aitken acceleration option is turned on. """ SOLVER = 'NL: NLBGS'
[docs] def __init__(self, **kwargs): """ Initialize all attributes. """ super().__init__(**kwargs) self._theta_n_1 = 1.0 self._delta_outputs_n_1 = None
def _setup_solvers(self, system, depth): """ Assign system instance, set depth, and optionally perform setup. Parameters ---------- system : <System> pointer to the owning system. depth : int depth of the current system (already incremented). """ super()._setup_solvers(system, depth) if len(system._subsystems_allprocs) != len(system._subsystems_myproc): raise RuntimeError('{}: Nonlinear Gauss-Seidel cannot be used on a ' 'parallel group.'.format(self.msginfo)) def _declare_options(self): """ Declare options before kwargs are processed in the init method. """ super()._declare_options() self.options.declare('use_aitken', types=bool, default=False, desc='set to True to use Aitken relaxation') self.options.declare('aitken_min_factor', default=0.1, desc='lower limit for Aitken relaxation factor') self.options.declare('aitken_max_factor', default=1.5, desc='upper limit for Aitken relaxation factor') self.options.declare('aitken_initial_factor', default=1.0, desc='initial value for Aitken relaxation factor') self.options.declare('cs_reconverge', types=bool, default=True, desc='When True, when this driver solves under a complex step, nudge ' 'the Solution vector by a small amount so that it reconverges.') self.options.declare('use_apply_nonlinear', types=bool, default=False, desc="Set to True to always call apply_nonlinear on the solver's " "system after solve_nonlinear has been called.") self.options.declare('reraise_child_analysiserror', types=bool, default=False, desc='When the option is true, a solver will reraise any ' 'AnalysisError that arises during subsolve; when false, it will ' 'continue solving.') def _iter_initialize(self): """ Perform any necessary pre-processing operations. Returns ------- float initial error. float error at the first iteration. """ system = self._system() if self.options['use_aitken']: self._delta_outputs_n_1 = system._outputs.asarray(copy=True) self._theta_n_1 = 1. # When under a complex step from higher in the hierarchy, sometimes the step is too small # to trigger reconvergence, so nudge the outputs slightly so that we always get at least # one iteration. if system.under_complex_step and self.options['cs_reconverge']: system._outputs += np.linalg.norm(system._outputs.asarray()) * 1e-10 # Execute guess_nonlinear if specified and # we have not restarted from a saved point if not self._restarted: system._guess_nonlinear() return super()._iter_initialize() def _single_iteration(self): """ Perform the operations in the iteration loop. """ system = self._system() outputs = system._outputs residuals = system._residuals use_aitken = self.options['use_aitken'] if use_aitken: aitken_min_factor = self.options['aitken_min_factor'] aitken_max_factor = self.options['aitken_max_factor'] # some variables that are used for Aitken's relaxation delta_outputs_n_1 = self._delta_outputs_n_1 theta_n_1 = self._theta_n_1 theta_n = self.options['aitken_initial_factor'] # store a copy of the outputs, used to compute the change in outputs later delta_outputs_n = outputs.asarray(copy=True) if use_aitken or not self.options['use_apply_nonlinear']: # store a copy of the outputs if not self.options['use_apply_nonlinear']: with system._unscaled_context(outputs=[outputs]): outputs_n = outputs.asarray(copy=True) else: outputs_n = outputs.asarray(copy=True) self._solver_info.append_subsolver() self._gs_iter() self._solver_info.pop() if use_aitken: # compute the change in the outputs after the NLBGS iteration delta_outputs_n -= outputs.asarray() delta_outputs_n *= -1 if self._iter_count >= 2: # Compute relaxation factor. This method is used by Kenway et al. in # "Scalable Parallel Approach for High-Fidelity Steady-State Aero- # elastic Analysis and Adjoint Derivative Computations" (ln 22 of Algo 1) temp = delta_outputs_n.copy() temp -= delta_outputs_n_1 # If MPI, piggyback on the residual vector to perform a distributed norm. if system.comm.size > 1: backup_r = residuals.asarray(copy=True) residuals.set_val(temp) temp_norm = residuals.get_norm() else: temp_norm = np.linalg.norm(temp) if temp_norm == 0.: temp_norm = 1e-12 # prevent division by 0 below # If MPI, piggyback on the output and residual vectors to perform a distributed # dot product. if system.comm.size > 1: backup_o = outputs.asarray(copy=True) outputs.set_val(delta_outputs_n) tddo = residuals.set_val(backup_r) outputs.set_val(backup_o) else: tddo = theta_n = theta_n_1 * (1 - tddo / temp_norm ** 2) else: # keep the initial the relaxation factor pass # limit relaxation factor to the specified range theta_n = max(aitken_min_factor, min(aitken_max_factor, theta_n)) # save relaxation factor for the next iteration self._theta_n_1 = theta_n if not self.options['use_apply_nonlinear']: with system._unscaled_context(outputs=[outputs]): outputs.set_val(outputs_n) else: outputs.set_val(outputs_n) # compute relaxed outputs outputs += theta_n * delta_outputs_n # save update to use in next iteration delta_outputs_n_1[:] = delta_outputs_n if not self.options['use_apply_nonlinear']: # Residual is the change in the outputs vector. with system._unscaled_context(outputs=[outputs], residuals=[residuals]): residuals.set_val(outputs.asarray() - outputs_n) def _run_apply(self): """ Run the apply_nonlinear method on the system. """ system = self._system() maxiter = self.options['maxiter'] itercount = self._iter_count if (maxiter < 2 and itercount < 1) or self.options['use_apply_nonlinear']: # This option runs apply_nonlinear to calculate the residuals, and thus ends up # executing ExplicitComponents twice per iteration. self._recording_iter.push(('_run_apply', 0)) try: system._apply_nonlinear() finally: self._recording_iter.pop() elif itercount < 1: # Run instead of calling apply, so that we don't "waste" the extra run. This also # further increments the iteration counter. self._iter_count += 1 outputs = system._outputs residuals = system._residuals with system._unscaled_context(outputs=[outputs]): outputs_n = outputs.asarray(copy=True) self._solver_info.append_subsolver() for subsys in system._solver_subsystem_iter(local_only=False): system._transfer('nonlinear', 'fwd', if subsys._is_local: subsys._solve_nonlinear() self._solver_info.pop() with system._unscaled_context(residuals=[residuals]): residuals.set_val(outputs.asarray() - outputs_n)