fdim.hpp

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#ifndef __STAN__AGRAD__REV__FDIM_HPP__
#define __STAN__AGRAD__REV__FDIM_HPP__

#include <stan/agrad/rev/var.hpp>
#include <stan/agrad/rev/op/vv_vari.hpp>
#include <stan/agrad/rev/op/v_vari.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() {
          avi_->adj_ += adj_;
          bvi_->adj_ -= adj_;
        }
      };

      class fdim_vd_vari : public op_v_vari {
      public:
        fdim_vd_vari(vari* avi, double b) :
          op_v_vari(avi->val_ - b, avi) {
        }
        void chain() {
          avi_->adj_ += adj_;
        }
      };

      class fdim_dv_vari : public op_v_vari {
      public:
        fdim_dv_vari(double a, vari* bvi) :
          op_v_vari(a - bvi->val_, bvi) {
        }
        void chain() {
          // avi_ is bvi argument to constructor
          avi_->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 fdim_dv_vari(a,b.vi_))
        : var(new vari(0.0));
    }

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

  }
}
#endif