fabs.hpp

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#ifndef STAN__AGRAD__REV__FUNCTIONS__FABS_HPP
#define STAN__AGRAD__REV__FUNCTIONS__FABS_HPP

#include <stan/agrad/rev/var.hpp>
#include <stan/agrad/rev/vari.hpp>
#include <stan/agrad/rev/internal/precomp_v_vari.hpp>
#include <stan/agrad/rev/operators/operator_unary_negative.hpp>
#include <stan/math/constants.hpp>


namespace stan {
  namespace agrad {
    
    inline var fabs(const var& a) {
      using stan::math::NOT_A_NUMBER;
      // cut-and-paste from abs()
      if (a.val() > 0.0)
        return a;
      else if (a.val() < 0.0)
        return var(new neg_vari(a.vi_));
      else if (a.val() == 0)
        return var(new vari(0));
      else
        return var(new precomp_v_vari(NOT_A_NUMBER,a.vi_,NOT_A_NUMBER));
    }

  }
}
#endif