atomic_four_rev_depend¶

Atomic Function Reverse Dependency¶

Syntax¶

You can define one or the other of the following callbacks, but you should not define both.

Preferred¶

ok = afun . rev_depend ( call_id ,
      ident_zero_x , depend_x , depend_y
)

Deprecated 2022-05-10¶

ok = afun . rev_depend ( call_id ,
      depend_x , depend_y
)

Prototype¶

template <class Base>
bool atomic_four<Base>::rev_depend(
   size_t                      call_id      ,
   const vector<bool>&         ident_zero_x ,
   vector<bool>&               depend_x     ,
   const vector<bool>&         depend_y     )

Dependency Analysis¶

This calculation is sometimes referred to as a reverse dependency analysis.

Implementation¶

This function must be defined if afun is used to define an ADFun object f , and f.optimize() is used.

Base¶

See Base .

vector¶

is the CppAD_vector template class.

call_id¶

See call_id .

ident_zero_x¶

This can sometimes be used to create more efficient dependency (fewer true values in depend_x ). If you do not see a way to do this, you can just ignore it. This argument has size equal to the number of arguments to this atomic function; i.e. the size of ax . If ident_zero_x [ j ] is true, the argument ax [ j ] is a constant parameter that is identically zero. An identically zero value times any other value can be treated as being identically zero.

depend_x¶

This vector has size equal to the number of arguments for this atomic function; i.e. n = ax . size () (see ax ). The input values of the elements of depend_x are not specified (must not matter). Upon return, for \(j = 0 , \ldots , n-1\), depend_x [ j ] is true if the values of interest depend on the value of ax [ j ] in the corresponding atomic function call.

Optimize¶

Parameters and variables, that the values of interest do not depend on, may get removed by optimization . The corresponding values in taylor_x (after optimization has removed them) are currently zero, but perhaps these should be changed back to nan.

depend_y¶

This vector has size equal to the number of results for this atomic function; i.e. m = ay . size () (see ay ). For \(i = 0 , \ldots , m-1\), depend_y [ i ] is true if the values of interest depend on the value of ay [ i ] in the corresponding atomic function call.

ok¶

If this calculation succeeded, ok is true. Otherwise, it is false.

Example¶

The following is an example rev_depend definition taken from atomic_four_norm_sq.cpp :

      bool rev_depend(
         size_t                                     call_id     ,
         CppAD::vector<bool>&                       depend_x    ,
         const CppAD::vector<bool>&                 depend_y    ) override
      {  size_t n = depend_x.size();
# ifndef NDEBUG
         size_t m = depend_y.size();
         assert( call_id == 0 );
         assert( m == 1 );
# endif
         for(size_t j = 0; j < n; ++j)
            depend_x[j] = depend_y[0];
         //
         return true;
      }