| Stan Math Library 2.11.0 reverse mode automatic differentiation

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stan::math::vari Class Reference

The variable implementation base class. More...

`#include <vari.hpp>`

Inheritance diagram for stan::math::vari:

## Public Member Functions
| vari (const double x)
| Construct a variable implementation from a value. More...
| vari (const double x, bool stacked)
virtual | ~vari ()
| Throw an illegal argument exception. More...
virtual void | chain ()
| Apply the chain rule to this variable based on the variables on which it depends. More...
void | init_dependent ()
| Initialize the adjoint for this (dependent) variable to 1. More...
void | set_zero_adjoint ()
| Set the adjoint value of this variable to 0. More...

## Static Public Member Functions
static void * | operator new (size_t nbytes)
| Allocate memory from the underlying memory pool. More...
static void | operator delete (void *)
| Delete a pointer from the underlying memory pool. More...

## Public Attributes
const double | val_
| The value of this variable. More...
double | adj_
| The adjoint of this variable, which is the partial derivative of this variable with respect to the root variable. More...

## Friends
class | var
std::ostream & | operator<< (std::ostream &os, const vari *v)
| Insertion operator for vari. More...

## Detailed Description

The variable implementation base class.

This class is complete (not abstract) and may be used for constants.

A variable implementation is constructed with a constant value. It also stores the adjoint for storing the partial derivative with respect to the root of the derivative tree.

The chain() method applies the chain rule. Concrete extensions of this class will represent base variables or the result of operations such as addition or subtraction. These extended classes will store operand variables and propagate derivative information via an implementation of chain().

Definition at line 30 of file vari.hpp.

## Constructor & Destructor Documentation

stan::math::vari::vari | ( | const double | x | ) |
| inlineexplicit

Construct a variable implementation from a value.

The adjoint is initialized to zero.

All constructed variables are added to the stack. Variables should be constructed before variables on which they depend to insure proper partial derivative propagation. During derivative propagation, the chain() method of each variable will be called in the reverse order of construction.

Parameters

  x | Value of the constructed variable.

Definition at line 58 of file vari.hpp.

stan::math::vari::vari | ( | const double | x,
|  | bool | stacked
| ) |  |
| inline

Definition at line 64 of file vari.hpp.

virtual stan::math::vari::~vari | ( |  | ) |
| inlinevirtual

Throw an illegal argument exception.

Warning: Destructors should never called for var objects.

Exceptions

  Logic | exception always.

Definition at line 80 of file vari.hpp.

## Member Function Documentation

virtual void stan::math::vari::chain | ( |  | ) |
| inlinevirtual

Apply the chain rule to this variable based on the variables on which it depends.

The base implementation in this class is a no-op.

Reimplemented in stan::math::precomputed_gradients_vari, stan::math::cholesky_decompose_v_vari, stan::math::stored_gradient_vari, stan::math::gevv_vvv_vari, stan::math::sum_v_vari, stan::math::scal_squared_distance_dv_vari, stan::math::scal_squared_distance_vd_vari, stan::math::precomp_vvv_vari, stan::math::precomp_vv_vari, stan::math::precomp_v_vari, and stan::math::scal_squared_distance_vv_vari.

Definition at line 89 of file vari.hpp.

void stan::math::vari::init_dependent | ( |  | ) |
| inline

Initialize the adjoint for this (dependent) variable to 1.

This operation is applied to the dependent variable before propagating derivatives, setting the derivative of the result with respect to itself to be 1.

Definition at line 98 of file vari.hpp.

static void stan::math::vari::operator delete | ( | void * |  | ) |
| inlinestatic

Delete a pointer from the underlying memory pool.

This no-op implementation enables a subclass to throw exceptions in its constructor. An exception thrown in the constructor of a subclass will result in an error being raised, which is in turn caught and calls delete().

See the discussion of "plugging the memory leak" in: http://www.parashift.com/c++-faq/memory-pools.html

Definition at line 149 of file vari.hpp.

static void* stan::math::vari::operator new | ( | size_t | nbytes | ) |
| inlinestatic

Allocate memory from the underlying memory pool.

This memory is is managed as a whole externally.

Warning: Classes should not be allocated with this operator if they have non-trivial destructors.

Parameters

  nbytes | Number of bytes to allocate.

Returns
  Pointer to allocated bytes.

Definition at line 134 of file vari.hpp.

void stan::math::vari::set_zero_adjoint | ( |  | ) |
| inline

Set the adjoint value of this variable to 0.

This is used to reset adjoints before propagating derivatives again (for example in a Jacobian calculation).

Definition at line 107 of file vari.hpp.

## Friends And Related Function Documentation

std::ostream& operator<< | ( | std::ostream & | os,
|  | const vari * | v
| ) |  |
| friend

Insertion operator for vari.

Prints the current value and the adjoint value.

Parameters

  os | [in, out] ostream to modify
  v | [in] vari object to print.

Returns
  The modified ostream.

Definition at line 120 of file vari.hpp.

friend class var
| friend

Definition at line 32 of file vari.hpp.

## Member Data Documentation

double stan::math::vari::adj_

The adjoint of this variable, which is the partial derivative of this variable with respect to the root variable.

Definition at line 44 of file vari.hpp.

const double stan::math::vari::val_

The value of this variable.

Definition at line 38 of file vari.hpp.

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

- stan/math/rev/core/vari.hpp

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