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src
Evolution
Systems
Cce
System.hpp
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// Distributed under the MIT License.
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// See LICENSE.txt for details.
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#pragma once
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/*!
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* \ingroup EvolutionSystemsGroup
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* \brief The set of utilities for performing Cauchy characteristic evolution
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* and Cauchy characteristic matching.
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*
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* \details Cauchy characteristic evolution (CCE) is a secondary nonlinear GR
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* evolution system that covers the domain extending from a spherical boundary
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* away from the strong-field regime, and extending all the way to future null
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* infinity \f$\mathcal I^+\f$. The evolution system is governed by five
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* hypersurface equations that are integrated radially along future null slices,
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* and one evolution equation that governs the evolution of one hypersurface to
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* the next.
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*
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* The mathematics of CCE are intricate, and SpECTRE's version implements a
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* number of tricks and improvements that are not yet present in other contexts.
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* For introductions to CCE generally, see papers \cite Bishop1997ik,
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* \cite Bishop1998uk, and \cite Barkett2019uae. Here we do not present a full
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* description of all of the mathematics, but instead just provide a high-level
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* roadmap of the SpECTRE utilities and how they come together in the CCE
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* system. This is intended as a map for maintainers of the codebase.
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*
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* First, worldtube data from a completed or running Cauchy evolution of the
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* Einstein field equations (currently the only one implemented in SpECTRE is
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* Generalized Harmonic) must be translated to Bondi spin-weighted scalars at
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* the extraction sphere. Relevant utilities for this conversion are
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* `Cce::WorldtubeDataManager`, `Cce::ReducedWorldtubeDataManager`,
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* `Cce::create_bondi_boundary_data`. Relevant parts of the parallel
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* infrastructure are `Cce::H5WorldtubeBoundary`,
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* `Cce::Actions::BoundaryComputeAndSendToEvolution`,
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* `Cce::Actions::RequestBoundaryData`, and
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* `Cce::Actions::ReceiveWorldtubeData`.
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*
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* The first hypersurface must be initialized with some reasonable starting
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* value for the evolved Bondi quantity \f$J\f$. There isn't a universal perfect
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* prescription for this, as a complete description would require, like the
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* Cauchy initial data problem, knowledge of the system arbitrarily far in the
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* past. A utility for assigning the initial data is `Cce::InitializeJ`.
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*
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* SpECTRE CCE is currently unique in implementing an additional gauge transform
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* after the worldtube boundary data is derived. This is performed to obtain an
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* asymptotically well-behaved gauge that is guaranteed to avoid logarithmic
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* behavior that has plagued other CCE implementations, and so that the
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* asymptotic computations can be as simple, fast, and reliable as possible.
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* Relevant utilities for the gauge transformation are
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* `Cce::GaugeAdjustedBoundaryValue` (see template specializations),
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* `Cce::GaugeUpdateTimeDerivatives`, `Cce::GaugeUpdateAngularFromCartesian`,
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* `Cce::GaugeUpdateJacobianFromCoordinates`, `Cce::GaugeUpdateInterpolator`,
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* `Cce::GaugeUpdateOmega`, and `Cce::InitializeGauge`.
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*
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* Next, the CCE system must evaluate the hypersurface differential equations.
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* There are five, in sequence, deriving \f$\beta, Q, U, W,\f$ and \f$H\f$. For
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* each of the five radial differential equations, first the products and
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* derivatives on the right-hand side must be evaluated, then the full
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* right-hand side of the equation must be computed, and finally the radial
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* differential equation is integrated. The equations have a hierarchical
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* structure, so the result for \f$\beta\f$ feeds into the radial differential
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* equation for \f$Q\f$, and both feed into \f$U\f$, and so on.
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*
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* Relevant utilities for computing the inputs to the hypersurface equations are
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* `Cce::PrecomputeCceDependencies` (see template specializations),
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* `Cce::mutate_all_precompute_cce_dependencies`, `Cce::PreSwshDerivatives` (see
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* template specializations), `Cce::mutate_all_pre_swsh_derivatives_for_tag`,
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* and `Cce::mutate_all_swsh_derivatives_for_tag`. There are a number of
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* typelists in `IntegrandInputSteps.hpp` that determine the set of quantities
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* to be evaluated in each of the five hypersurface steps.
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* Once the hypersurface equation inputs are computed, then a hypersurface
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* equation right-hand side can be evaluated via `Cce::ComputeBondiIntegrand`
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* (see template specializations). Then, the hypersurface equation may be
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* integrated via `Cce::RadialIntegrateBondi` (see template specializations).
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*
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* Relevant parts of the parallel infrastructure for performing the hypersurface
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* steps are: `Cce::CharacteristicEvolution`,
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* `Cce::Actions::CalculateIntegrandInputsForTag`, and
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* `Cce::Actions::PrecomputeGlobalCceDependencies`. Note that most of the
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* algorithmic steps are laid out in order in the phase-dependent action list of
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* `Cce::CharacteristicEvolution`.
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*
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* The time integration for the hyperbolic part of the CCE equations is
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* performed via \f$\partial_u J = H\f$, where \f$\partial_u\f$ represents
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* differentiation with respect to retarded time at fixed numerical radius
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* \f$y\f$.
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*
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* At this point, all of the Bondi quantities on a given hypersurface have been
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* evaluated, and we wish to output the relevant waveform quantities at
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* \f$\mathcal I^+\f$. This acts much like an additional step in the
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* hypersurface sequence, with inputs that need to be calculated before the
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* quantities of interest can be evaluated. The action
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* `Cce::Actions::CalculateScriInputs` performs the sequence of steps to obtain
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* those inputs, and the utilities `Cce::CalculateScriPlusValue` (see template
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* specializations) can be used to evaluate the desired outputs at
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* \f$\mathcal I^+\f$.
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*
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* Unfortunately, those quantities at \f$\mathcal I^+\f$ are not yet an
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* appropriate waveform output, because the time coordinate with which they are
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* evaluated is the simulation time, not an asymptotically inertial time. So,
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* instead of directly writing the waveform outputs, we must put them in a queue
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* to be interpolated once enough data points have been accumulated to perform a
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* reliable interpolation at a consistent cut of \f$\mathcal I^+\f$ at constant
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* inertial time. Utilities for calculating and evolving the asymptotic inertial
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* time are `Cce::InitializeScriPlusValue` and `Cce::CalculateScriPlusValue`
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* using arguments involving `Cce::Tags::InertialRetardedTime`. A utility for
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* managing the interpolation is `Cce::ScriPlusInterpolationManager`, and
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* relevant parts of the parallel infrastructure for manipulating the data into
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* the interpolator and writing the results to disk are
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* `Cce::Actions::InsertInterpolationScriData` and
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* `Cce::Actions::ScriObserveInterpolated`.
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*
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*/
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namespace
Cce
{
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struct
System
{
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using
variables_tag
=
::Tags::Variables<Tags::BondiJ>
;
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};
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}
Cce::System
Definition:
System.hpp:116
Tags::Variables
Definition:
VariablesTag.hpp:21
Cce
The set of utilities for performing Cauchy characteristic evolution and Cauchy characteristic matchin...
Definition:
BoundaryComputeAndSendToEvolution.hpp:28
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