codi::InternalAdjointsInterface< T_Gradient, T_Identifier, T_Tape > Struct Template Reference

Abstracts the internal set of adjoint variables provided as part of the tape. More...

#include <internalAdjointsInterface.hpp>

Inheritance diagram for codi::InternalAdjointsInterface< T_Gradient, T_Identifier, T_Tape >:

Public Types
using	Gradient = T_Gradient
	See InternalAdjointsInterface.
using	Identifier = T_Identifier
	See InternalAdjointsInterface.
using	Tape = T_Tape
	See InternalAdjointsInterface.

Public Member Functions
void	beginUse ()
	Declare that the adjoints are in use, e.g., during a tape evaluation, and cannot be resized right now.
Gradient *	data ()
	Pointer to an underlying array implementation.
void	endUse ()
	Declare that the adjoints are no longer occupied.
	InternalAdjointsInterface (size_t initialSize)
Gradient &	operator[] (Identifier const &identifier)
	Reference access to the adjoint variable identified by identifier.
Gradient const &	operator[] (Identifier const &identifier) const
	Constant reference access to the adjoint variable identified by identifier.
void	resize (Identifier const &newSize)
	Ensure that identifiers up to newSize can be passed to operator[] without error.
size_t	size () const
	Returns the number of adjoint variables. Internally, declares usage of the adjoints.
template<typename Impl >
void	swap (Impl &other)
	Swap two sets of adjoint variables. Internally, declares usage of the adjoints.
void	zeroAll ()
	Set all adjoint variables to Gradient().

Detailed Description

template<typename T_Gradient, typename T_Identifier, typename T_Tape>
struct codi::InternalAdjointsInterface< T_Gradient, T_Identifier, T_Tape >

Abstracts the internal set of adjoint variables provided as part of the tape.

This interface describes the interaction between a tape and its associated adjoint variables as well as the state of the adjoint variables. Details on how the adjoint variables are implemented are abstracted away by this interface.

The adjoint variables can be read and written, resized, zeroed, and swapped. The number of adjoint variables can be queried, and, if applicable, a raw pointer to an underlying array implementation can be obtained.

The set of adjoint variables can be "in use" or "not in use". The adjoint variables are "in use" whenever there is read or write access to adjoint variables, or when any general property of the set of adjoint variables such as size is queried. The implementations of this interface ensure mutual exclusion between the "in use" state and reallocations of the set of adjoint variables due to resizing. Resizing is only allowed if the adjoint variables are "not in use". The implementations of data() and size() are expected to declare usage internally, if needed. For performance reasons, the operator[]() accessors and zeroAll() don't declare usage internally. Instead, the tape is responsible for this. It should declare usage by calls to beginUse() and endUse(). This way, multiple such calls can be safeguarded by a single usage declaration.

The tape must not call resize() as long as it has declared usage.

To give an example, tape evaluation involves multiple operator[]() calls. Prior to the evaluation, the tape ensures that the set of adjoint variables is sufficiently large. It calls beginUse() before the evaluation and endUse() after it. During the evaluation, no further resizing of the set of adjoint variables takes place.

See codi::DataManagementTapeInterface for a multithreading perspective on the "in use" mechanism.

A tape that maintains its adjoints internally against this interface can easily exchange the adjoint implementation. The principle use case of this interface is, at the moment, replacing a classical, tape-local adjoint vector by a thread-safe global one for use in a shared-memory parallel setting, see LocalAdjoints and ThreadSafeGlobalAdjoints.

Template Parameters

T_Gradient	The gradient type of a tape, usually chosen as ActiveType::Gradient.
T_Identifier	The adjoint/tangent identification of a tape, usually chosen as ActiveType::Identifier.
T_Tape	The associated tape type.

Constructor & Destructor Documentation

InternalAdjointsInterface()

template<typename T_Gradient , typename T_Identifier , typename T_Tape >

codi::InternalAdjointsInterface< T_Gradient, T_Identifier, T_Tape >::InternalAdjointsInterface ( size_t initialSize )

inline

Constructor

Parameters

initialSize

Initial number of adjoint variables.

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The documentation for this struct was generated from the following file:

• include/codi/tapes/misc/internalAdjointsInterface.hpp