codi::PositionalEvaluationTapeInterface< T_Position > Struct Template Reference

Reverse AD evaluation for parts of a recorded tape. More...

#include <positionalEvaluationTapeInterface.hpp>

Inheritance diagram for codi::PositionalEvaluationTapeInterface< T_Position >:

Public Types
using	Position = T_Position
	See PositionalEvaluationTapeInterface.

Public Member Functions
Interface definition
void	evaluate (Position const &start, Position const &end, AdjointsManagement adjointsManagement=AdjointsManagement::Automatic)
	Perform a reverse evaluation for a part of the tape. It hast to hold start >= end.
void	clearAdjoints (Position const &start, Position const &end, AdjointsManagement adjointsManagement=AdjointsManagement::Automatic)
	Clear all adjoints that would be set in a tape evaluation from start to end. It has to hold start >= end.
Position	getPosition () const
	Current position of the tape.
Position	getZeroPosition () const
	Initial position of the tape.
void	resetTo (Position const &pos, bool resetAdjoints=true, AdjointsManagement adjointsManagement=AdjointsManagement::Automatic)
	Reset the tape to the provided position.

Detailed Description

template<typename T_Position>
struct codi::PositionalEvaluationTapeInterface< T_Position >

Reverse AD evaluation for parts of a recorded tape.

See Tape Interface Design for a general overview of the tape interface design in CoDiPack.

The definitions in the ReverseTapeInterface provide only methods that operate on the full tape. With the methods in this interface, all these operations can be performed on parts of the tape.

Here is an example for a positional tape evaluation (Example 3 - Positional tape evaluations):

using Real = codi::RealReverse;
using Gradient = typename Real::Gradient;
using Tape = typename Real::Tape;
using Position = typename Tape::Position;
 
Real funcInner(Real x, Real y) {
  return sqrt(x * x + y * y);
}
 
void positionalExample() {
 
  Tape& tape = Real::getTape();
 
  // Recording
  Real a = 10.0;
  Real b = 4.0;
 
  tape.setActive();
  tape.registerInput(a);
  tape.registerInput(b);
 
  Real u1 = a + b;
  Real u2 = a - b;
 
  // Now comes a really long and complicated function. Tape it, reverse it and then store the result on the tape.
  // Step 1: Store the position
  Position begin = tape.getPosition();
 
  // Record the function
  Real w = funcInner(u1, u2);
 
  // Step 2: Reverse part of the tape
  w.gradient() = 1.0;
  tape.evaluate(tape.getPosition(), begin);
  Gradient u1_d = u1.gradient();
  Gradient u2_d = u2.gradient();
 
  // Step 3: Cleanup the reversal
  tape.resetTo(begin);
  u1.gradient() = Gradient();
  u2.gradient() = Gradient();
 
  // Now store the computed gradient data
  tape.storeManual(w.value(), w.getIdentifier(), 2);
  tape.pushJacobianManual(u1_d, u1.value(), u1.getIdentifier());
  tape.pushJacobianManual(u2_d, u2.value(), u2.getIdentifier());
 
  Real y = cos(w);
 
  tape.registerOutput(y);
  tape.setPassive();
 
  // Reverse evaluation
  y.setGradient(1.0);
  tape.evaluate();
 
  std::cout << "Positional example:" << std::endl;
  std::cout << "Gradient of dy/da: " << a.getGradient() << std::endl;
  std::cout << "Gradient of dy/db: " << b.getGradient() << std::endl;
 
  tape.reset();
}

Template Parameters

T_Position

Global tape position, usually chosen as Tape::Position.

Member Function Documentation

clearAdjoints()

template<typename T_Position >

void codi::PositionalEvaluationTapeInterface< T_Position >::clearAdjoints	(	Position const &	start,
		Position const &	end,
		AdjointsManagement	adjointsManagement = AdjointsManagement::Automatic )

Clear all adjoints that would be set in a tape evaluation from start to end. It has to hold start >= end.

Automatic adjoints management involves locking, see AdjointsManagement for details.

evaluate()

template<typename T_Position >

void codi::PositionalEvaluationTapeInterface< T_Position >::evaluate	(	Position const &	start,
		Position const &	end,
		AdjointsManagement	adjointsManagement = AdjointsManagement::Automatic )

Perform a reverse evaluation for a part of the tape. It hast to hold start >= end.

Automatic adjoints management involves bounds checking, resizing, and locking, see AdjointsManagement for details.

resetTo()

template<typename T_Position >

void codi::PositionalEvaluationTapeInterface< T_Position >::resetTo	(	Position const &	pos,
		bool	resetAdjoints = true,
		AdjointsManagement	adjointsManagement = AdjointsManagement::Automatic )

Reset the tape to the provided position.

Automatic adjoints management involves locking, see AdjointsManagement for details.

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

• include/codi/tapes/interfaces/positionalEvaluationTapeInterface.hpp