Source code for openmdao.approximation_schemes.complex_step

"""Complex Step derivative approximations."""

from collections import defaultdict

import numpy as np

from openmdao.utils.om_warnings import issue_warning, DerivativesWarning
from openmdao.approximation_schemes.approximation_scheme import ApproximationScheme


[docs]class ComplexStep(ApproximationScheme): r""" Approximation scheme using complex step to calculate derivatives. For example, using a step size of 'h' will approximate the derivative in the following way: .. math:: f'(x) = \Im{\frac{f(x+ih)}{h}}. Attributes ---------- _fd : <FiniteDifference> When nested complex step is detected, we switch to Finite Difference. """ DEFAULT_OPTIONS = { 'step': 1e-40, 'directional': False, }
[docs] def __init__(self): """ Initialize the ApproximationScheme. """ super().__init__() # Only used when nested under complex step. self._fd = None
[docs] def add_approximation(self, abs_key, system, kwargs, vector=None): """ Use this approximation scheme to approximate the derivative d(of)/d(wrt). Parameters ---------- abs_key : tuple(str,str) Absolute name pairing of (of, wrt) for the derivative. system : System Containing System. vector : ndarray or None Direction for difference when using directional derivatives. kwargs : dict Additional keyword arguments, to be interpreted by sub-classes. """ options = self.DEFAULT_OPTIONS.copy() options.update(kwargs) options['vector'] = vector wrt = abs_key[1] if wrt in self._wrt_meta: self._wrt_meta[wrt].update(options) else: self._wrt_meta[wrt] = options self._reset() # force later regen of approx_groups
def _get_approx_data(self, system, wrt, meta): """ Given approximation metadata, compute necessary delta for complex step. Parameters ---------- system : System System whose derivatives are being approximated. wrt : str Name of wrt variable. meta : dict Metadata dict. Returns ------- float Delta needed for complex step perturbation. """ step = meta['step'] step *= 1j return step
[docs] def compute_approx_col_iter(self, system, under_cs=False): """ Execute the system to compute the approximate sub-Jacobians. Parameters ---------- system : System System on which the execution is run. under_cs : bool True if we're currently under complex step at a higher level. """ if not self._wrt_meta: return if system.under_complex_step: # If we are nested under another complex step, then warn and swap to FD. if not self._fd: from openmdao.approximation_schemes.finite_difference import FiniteDifference issue_warning("Nested complex step detected. Finite difference will be used.", prefix=system.pathname, category=DerivativesWarning) fd = self._fd = FiniteDifference() empty = {} for wrt in self._wrt_meta: fd.add_approximation(wrt, system, empty) yield from self._fd.compute_approx_col_iter(system) return saved_inputs = system._inputs._get_data().copy() system._inputs._data.imag[:] = 0.0 saved_outputs = system._outputs.asarray(copy=True) system._outputs._data.imag[:] = 0.0 saved_resids = system._residuals.asarray(copy=True) system._residuals._data.imag[:] = 0.0 # Turn on complex step. system._set_complex_step_mode(True) try: yield from self._compute_approx_col_iter(system, under_cs=True) finally: # Turn off complex step. system._set_complex_step_mode(False) system._inputs.set_val(saved_inputs) system._outputs.set_val(saved_outputs) system._residuals.set_val(saved_resids)
def _get_multiplier(self, delta): """ Return a multiplier to be applied to the jacobian. Parameters ---------- delta : complex Complex number used to compute the multiplier. Returns ------- float multiplier to apply to the jacobian. """ return (1.0 / delta * 1j).real def _transform_result(self, array): """ Return the imaginary part of the given array. Parameters ---------- array : ndarray of complex Result array after doing a complex step. Returns ------- ndarray Imaginary part of the result array. """ return array.imag def _run_point(self, system, idx_info, delta, result_array, total): """ Perturb the system inputs with a complex step, run, and return the results. Parameters ---------- system : System The system having its derivs approximated. idx_info : tuple of (Vector, ndarray of int) Tuple of wrt indices and corresponding data vector to perturb. delta : complex Perturbation amount. result_array : ndarray An array used to store the results. total : bool If True total derivatives are being approximated, else partials. Returns ------- ndarray Copy of the outputs or residuals array after running the perturbed system. """ for vec, idxs in idx_info: if vec is not None and idxs is not None: vec.iadd(delta, idxs) if total: system.run_solve_nonlinear() result_array[:] = system._outputs.asarray() else: system.run_apply_nonlinear() result_array[:] = system._residuals.asarray() for vec, idxs in idx_info: if vec is not None and idxs is not None: vec.isub(delta, idxs) return result_array
[docs] def apply_directional(self, data, direction): """ Apply stepsize to direction and embed into approximation data. Parameters ---------- data : float Step size for complex step. direction : ndarray Vector containing derivative direction. Returns ------- ndarray New step direction. """ return data * direction