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// SPDX-License-Identifier: EPL-2.0 OR GPL-2.0-or-later
// SPDX-FileCopyrightText: Bradley M. Bell <bradbell@seanet.com>
// SPDX-FileContributor: 2003-22 Bradley M. Bell
// ----------------------------------------------------------------------------
/*
{xrst_begin atomic_three_get_started.cpp}
Getting Started with Atomic Functions: Example and Test
#######################################################
Purpose
*******
This example demonstrates the minimal amount of information
necessary for a :ref:`atomic_three-name` function.
Start Class Definition
**********************
{xrst_spell_off}
{xrst_code cpp} */
# include <cppad/cppad.hpp> // CppAD include file
namespace { // start empty namespace
using CppAD::vector; // abbreviate CppAD::vector using vector
// start definition of atomic derived class using atomic_three interface
class atomic_get_started : public CppAD::atomic_three<double> {
/* {xrst_code}
{xrst_spell_on}
Constructor
***********
{xrst_spell_off}
{xrst_code cpp} */
public:
// can use const char* name when calling this constructor
atomic_get_started(const std::string& name) : // can have more arguments
CppAD::atomic_three<double>(name) // inform base class of name
{ }
private:
/* {xrst_code}
{xrst_spell_on}
for_type
********
{xrst_spell_off}
{xrst_code cpp} */
// calculate type_y
bool for_type(
const vector<double>& parameter_x ,
const vector<CppAD::ad_type_enum>& type_x ,
vector<CppAD::ad_type_enum>& type_y ) override
{ assert( parameter_x.size() == type_x.size() );
bool ok = type_x.size() == 1; // n
ok &= type_y.size() == 1; // m
if( ! ok )
return false;
type_y[0] = type_x[0];
return true;
}
/* {xrst_code}
{xrst_spell_on}
forward
*******
{xrst_spell_off}
{xrst_code cpp} */
// forward mode routine called by CppAD
bool forward(
const vector<double>& parameter_x ,
const vector<CppAD::ad_type_enum>& type_x ,
size_t need_y ,
size_t order_low ,
size_t order_up ,
const vector<double>& taylor_x ,
vector<double>& taylor_y ) override
{
# ifndef NDEBUG
size_t n = taylor_x.size() / (order_up + 1);
size_t m = taylor_y.size() / (order_up + 1);
# endif
assert( n == 1 );
assert( m == 1 );
assert( order_low <= order_up );
// return flag
bool ok = order_up == 0;
if( ! ok )
return ok;
// Order zero forward mode.
// This case must always be implemented
// y^0 = g( x^0 ) = 1 / x^0
taylor_y[0] = 1. / taylor_x[0];
//
return ok;
}
/* {xrst_code}
{xrst_spell_on}
End Class Definition
********************
{xrst_spell_off}
{xrst_code cpp} */
}; // End of atomic_get_started class
} // End empty namespace
/* {xrst_code}
{xrst_spell_on}
Use Atomic Function
*******************
{xrst_spell_off}
{xrst_code cpp} */
bool get_started(void)
{ bool ok = true;
using CppAD::AD;
using CppAD::NearEqual;
double eps = 10. * CppAD::numeric_limits<double>::epsilon();
/* {xrst_code}
{xrst_spell_on}
Constructor
===========
{xrst_spell_off}
{xrst_code cpp} */
// Create the atomic get_started object corresponding to g(x)
atomic_get_started afun("atomic_get_started");
/* {xrst_code}
{xrst_spell_on}
Recording
=========
{xrst_spell_off}
{xrst_code cpp} */
// Create the function f(x) which is eqaul to g(x) for this example.
//
// domain space vector
size_t n = 1;
double x0 = 0.5;
CPPAD_TESTVECTOR( AD<double> ) ax(n);
ax[0] = x0;
// declare independent variables and start tape recording
CppAD::Independent(ax);
// range space vector
size_t m = 1;
CPPAD_TESTVECTOR( AD<double> ) ay(m);
// call atomic function and store result in au[0]
// u = 1 / x
CPPAD_TESTVECTOR( AD<double> ) au(m);
afun(ax, au);
// now use AD division to invert to invert the operation
ay[0] = 1.0 / au[0]; // y = 1 / u = x
// create f: x -> y and stop tape recording
CppAD::ADFun<double> f;
f.Dependent (ax, ay); // f(x) = x
/* {xrst_code}
{xrst_spell_on}
forward
=======
{xrst_spell_off}
{xrst_code cpp} */
// check function value
double check = x0;
ok &= NearEqual( Value(ay[0]) , check, eps, eps);
// check zero order forward mode
size_t q;
CPPAD_TESTVECTOR( double ) x_q(n), y_q(m);
q = 0;
x_q[0] = x0;
y_q = f.Forward(q, x_q);
ok &= NearEqual(y_q[0] , check, eps, eps);
/* {xrst_code}
{xrst_spell_on}
Return Test Result
==================
{xrst_spell_off}
{xrst_code cpp} */
return ok;
}
/* {xrst_code}
{xrst_spell_on}
{xrst_end atomic_three_get_started.cpp}
*/
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