erf.hpp

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#ifndef STAN__AGRAD__REV__FUNCTIONS__ERF_HPP
#define STAN__AGRAD__REV__FUNCTIONS__ERF_HPP

#include <valarray>
#include <math.h>
#include <stan/agrad/rev/var.hpp>
#include <stan/agrad/rev/internal/v_vari.hpp>
#include <stan/math/constants.hpp>

namespace stan {
  namespace agrad {

    namespace {
      class erf_vari : public op_v_vari {
      public:
        erf_vari(vari* avi) :
          op_v_vari(::erf(avi->val_),avi) {
        }
        void chain() {
          avi_->adj_ += adj_ * stan::math::TWO_OVER_SQRT_PI 
            * ::exp(- avi_->val_ * avi_->val_);
        }
      };
    }

    inline var erf(const stan::agrad::var& a) {
      return var(new erf_vari(a.vi_));
    }

  }
}
#endif