\(\newcommand{\W}[1]{ \; #1 \; }\) \(\newcommand{\R}[1]{ {\rm #1} }\) \(\newcommand{\B}[1]{ {\bf #1} }\) \(\newcommand{\D}[2]{ \frac{\partial #1}{\partial #2} }\) \(\newcommand{\DD}[3]{ \frac{\partial^2 #1}{\partial #2 \partial #3} }\) \(\newcommand{\Dpow}[2]{ \frac{\partial^{#1}}{\partial {#2}^{#1}} }\) \(\newcommand{\dpow}[2]{ \frac{ {\rm d}^{#1}}{{\rm d}\, {#2}^{#1}} }\)

base2vec_ad.cpp

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Using base2ad and VecAD together: Example and Test

Purpose

This example demonstrate that base2ad does not convert VecAD operations as might be expected. To be specific, this indexing into a VecAD object gets fixed when zero order forward mode is run for a base2ad result; e.g. af below.

# include <cppad/cppad.hpp>

bool base2vec_ad(void)
{  using CppAD::vector;
   using CppAD::AD;
   //
   bool ok = true;
   //
   // f(x) = x[0] if 0 <= x[2] < 1
   //      = x[1] if 1 <= x[2] < 2
   vector< AD<double> > ax(3), ay(1);
   ax[0] = 3.0;
   ax[1] = 2.0;
   ax[2] = 1.0;
   Independent(ax);
   CppAD::VecAD<double> av(2);
   av[ AD<double>(0) ] = ax[0];
   av[ AD<double>(1) ] = ax[1];
   ay[0] = av[ ax[2] ];
   CppAD::ADFun<double> f(ax, ay);
   //
   // ok
   // value during recording of f
   ok &= ay[0] == ax[1];
   //
   // ok
   // f zero order forward mode, the VecAD commands give expected result
   vector<double> x(3), y(1);
   x[0] = 2.0;
   x[1] = 1.0;
   x[2] = 0.0;
   y = f.Forward(0, x);
   ok &= y[0] == x[0];
   //
   // af
   CppAD::ADFun< AD<double>, double > af = f.base2ad();
   //
   // g
   ax[0] = 3.0;
   ax[1] = 2.0;
   ax[2] = 1.0;
   Independent(ax);
   ay = af.Forward(0, ax);
   CppAD::ADFun<double> g(ax, ay);
   //
   // ok
   // value during recording of g
   ok &= ay[0] == ax[1];
   //
   // ok
   // g zero order forward mode
   // Note that this index does not change, but the value does
   x[0] = 5.0;
   x[1] = 4.0;
   x[2] = 0.0;
   y = g.Forward(0, x);
   ok &= y[0] == x[1];
   //
   return ok;
}