vari.hpp

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#ifndef __STAN__AGRAD__REV__VARI_HPP__
#define __STAN__AGRAD__REV__VARI_HPP__

#include <ostream>

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

namespace stan {
  namespace agrad {
    
    // forward declaration of var
    class var;

    class vari : public chainable {
    private:
      friend class var;

    public: 

      const double val_;

      double adj_;
      
      vari(const double x): 
        val_(x),
        adj_(0.0) {
        var_stack_.push_back(this);
      }

      vari(const double x,bool stacked): 
        val_(x),
        adj_(0.0) {
        if (stacked)
          var_stack_.push_back(this);
        else
          var_nochain_stack_.push_back(this);
      }
      
      ~vari() { 
        // throw std::logic_error("vari destruction handled automatically");
      }

      virtual void init_dependent() {
        adj_ = 1.0;   // droot/droot = 1
      }

      virtual void set_zero_adjoint() {
        adj_ = 0.0;
      }

      friend std::ostream& operator<<(std::ostream& os, const vari* v) {
        return os << v << "  " << v->val_ << " : " << v->adj_;
      }
    };

  }
}
#endif