chainable.hpp

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#ifndef STAN__AGRAD__REV__CHAINABLE_HPP
#define STAN__AGRAD__REV__CHAINABLE_HPP

#include <vector>
#include <stan/agrad/rev/var_stack.hpp>

namespace stan {
  namespace agrad {

    class chainable {

    public:

      chainable() { }

      virtual ~chainable() {
        // handled automatically
      }

      virtual void chain() {
      }

      virtual void init_dependent() {
      }

      virtual void set_zero_adjoint() {
      }

      static inline void* operator new(size_t nbytes) {
        return memalloc_.alloc(nbytes);
      }

      static inline void operator delete(void* /* ignore arg */) {
        /* no op */
      }
    };

    
    
    static void set_zero_all_adjoints() {
      for (size_t i = 0; i < var_stack_.size(); ++i)
        var_stack_[i]->set_zero_adjoint();
      for (size_t i = 0; i < var_nochain_stack_.size(); ++i)
        var_nochain_stack_[i]->set_zero_adjoint();
    }

    static void grad(chainable* vi) {

      // simple reference implementation (intended as doc):
      //   vi->init_dependent(); 
      //   size_t end = var_stack_.size();
      //   size_t begin = empty_nested() ? 0 : end - nested_size();
      //   for (size_t i = end; --i > begin; )  
      //     var_stack_[i]->chain();

      typedef std::vector<chainable*>::reverse_iterator it_t;
      vi->init_dependent(); 
      it_t begin = var_stack_.rbegin();
      it_t end = empty_nested() ? var_stack_.rend() : begin + nested_size();
      for (it_t it = begin; it < end; ++it) {
        (*it)->chain();
      }
    }

  }
}
#endif