fdim.hpp

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#ifndef STAN__AGRAD__REV__FUNCTIONS__FDIM_HPP
#define STAN__AGRAD__REV__FUNCTIONS__FDIM_HPP

#include <stan/agrad/rev/var.hpp>
#include <stan/agrad/rev/internal/vv_vari.hpp>
#include <stan/agrad/rev/internal/vd_vari.hpp>
#include <stan/agrad/rev/internal/dv_vari.hpp>
#include <boost/math/special_functions/fpclassify.hpp>
#include <stan/meta/likely.hpp>

namespace stan {
  namespace agrad {

    namespace {
      class fdim_vv_vari : public op_vv_vari {
      public:
        fdim_vv_vari(vari* avi, vari* bvi) :
          op_vv_vari(avi->val_ - bvi->val_, avi, bvi) {
        }
        void chain() {
          if (unlikely(boost::math::isnan(avi_->val_)
                       || boost::math::isnan(bvi_->val_))) {
            avi_->adj_ = std::numeric_limits<double>::quiet_NaN();
            bvi_->adj_ = std::numeric_limits<double>::quiet_NaN();
          } else {
            avi_->adj_ += adj_;
            bvi_->adj_ -= adj_;
          }
        }
      };

      class fdim_vd_vari : public op_vd_vari {
      public:
        fdim_vd_vari(vari* avi, double b) :
          op_vd_vari(avi->val_ - b, avi,b) {
        }
        void chain() {
          if (unlikely(boost::math::isnan(avi_->val_)
                       || boost::math::isnan(bd_)))
            avi_->adj_ = std::numeric_limits<double>::quiet_NaN();
          else
            avi_->adj_ += adj_;
        }
      };

      class fdim_dv_vari : public op_dv_vari {
      public:
        fdim_dv_vari(double a, vari* bvi) :
          op_dv_vari(a - bvi->val_, a,bvi) {
        }
        void chain() {
          if (unlikely(boost::math::isnan(bvi_->val_)
                       || boost::math::isnan(ad_)))
            bvi_->adj_ = std::numeric_limits<double>::quiet_NaN();
          else
            bvi_->adj_ -= adj_;
        }
      };
    }

    inline var fdim(const stan::agrad::var& a,
                    const stan::agrad::var& b) {
      if (!(a.vi_->val_ <= b.vi_->val_))
        return var(new fdim_vv_vari(a.vi_,b.vi_));
      else
        return var(new vari(0.0));
    }

    inline var fdim(const double& a,
                    const stan::agrad::var& b) {
      return a <= b.vi_->val_
        ? var(new vari(0.0))
        : var(new fdim_dv_vari(a,b.vi_));
    }

    inline var fdim(const stan::agrad::var& a,
                    const double& b) {
      return a.vi_->val_ <= b
        ? var(new vari(0.0))
        : var(new fdim_vd_vari(a.vi_,b));
    }

  }
}
#endif