Emily Boudreaux
856ab51b4c
we need an autodiff library at some point (or we need to roll our own but I do not think that makes sense). CppAD is well tested and header only and easy to include. It is also Liscene compatible with GPL v3.0. Here we bring it in as a dependency
133 lines
3.4 KiB
C++
133 lines
3.4 KiB
C++
# ifndef CPPAD_CORE_ABS_HPP
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# define CPPAD_CORE_ABS_HPP
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/* --------------------------------------------------------------------------
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CppAD: C++ Algorithmic Differentiation: Copyright (C) 2003-20 Bradley M. Bell
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CppAD is distributed under the terms of the
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Eclipse Public License Version 2.0.
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This Source Code may also be made available under the following
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Secondary License when the conditions for such availability set forth
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in the Eclipse Public License, Version 2.0 are satisfied:
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GNU General Public License, Version 2.0 or later.
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---------------------------------------------------------------------------- */
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/*
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-------------------------------------------------------------------------------
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$begin abs$$
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$spell
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fabs
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Vec
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std
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faq
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Taylor
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Cpp
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namespace
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const
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abs
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$$
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$section AD Absolute Value Functions: abs, fabs$$
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$head Syntax$$
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$icode%y% = abs(%x%)
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%$$
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$icode%y% = fabs(%x%)%$$
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$head x, y$$
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See the $cref/possible types/unary_standard_math/Possible Types/$$
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for a unary standard math function.
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$head Atomic$$
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In the case where $icode x$$ is an AD type,
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this is an $cref/atomic operation/glossary/Operation/Atomic/$$.
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$head Complex Types$$
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The functions $code abs$$ and $icode fabs$$
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are not defined for the base types
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$code std::complex<float>$$ or $code std::complex<double>$$
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because the complex $code abs$$ function is not complex differentiable
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(see $cref/complex types faq/Faq/Complex Types/$$).
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$head Derivative$$
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CppAD defines the derivative of the $code abs$$ function is
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the $cref sign$$ function; i.e.,
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$latex \[
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{\rm abs}^{(1)} ( x ) = {\rm sign} (x ) =
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\left\{ \begin{array}{rl}
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+1 & {\rm if} \; x > 0 \\
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0 & {\rm if} \; x = 0 \\
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-1 & {\rm if} \; x < 0
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\end{array} \right.
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\] $$
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The result for $icode%x% == 0%$$ used to be a directional derivative.
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$head Example$$
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$children%
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example/general/fabs.cpp
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%$$
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The file
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$cref fabs.cpp$$
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contains an example and test of this function.
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$end
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-------------------------------------------------------------------------------
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*/
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// BEGIN CppAD namespace
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namespace CppAD {
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template <class Base>
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AD<Base> AD<Base>::abs_me (void) const
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{
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AD<Base> result;
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result.value_ = abs(value_);
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CPPAD_ASSERT_UNKNOWN( Parameter(result) );
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// check if there is a recording in progress
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local::ADTape<Base>* tape = AD<Base>::tape_ptr();
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if( tape == nullptr )
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return result;
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// check if operand is a constant parameter
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if( tape_id_ != tape->id_ )
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return result;
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if(ad_type_ == dynamic_enum)
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{ // dynamic paramter argument
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result.taddr_ = tape->Rec_.put_dyn_par(
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result.value_, local::abs_dyn, taddr_
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);
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result.tape_id_ = tape_id_;
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result.ad_type_ = dynamic_enum;
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}
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else
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{ // variable argument
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CPPAD_ASSERT_UNKNOWN( local::NumRes(local::AbsOp) == 1 );
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CPPAD_ASSERT_UNKNOWN( local::NumArg(local::AbsOp) == 1 );
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// corresponding operand address
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tape->Rec_.PutArg(taddr_);
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// put operator in the tape
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result.taddr_ = tape->Rec_.PutOp(local::AbsOp);
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// make result a variable
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result.tape_id_ = tape_id_;
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result.ad_type_ = variable_enum;
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}
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return result;
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}
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template <class Base>
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AD<Base> abs(const AD<Base> &x)
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{ return x.abs_me(); }
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template <class Base>
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AD<Base> abs(const VecAD_reference<Base> &x)
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{ return x.ADBase().abs_me(); }
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} // END CppAD namespace
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# endif
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