atan.hpp

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#ifndef __STAN__AGRAD__REV__ATAN_HPP__
#define __STAN__AGRAD__REV__ATAN_HPP__

#include <valarray>
#include <stan/agrad/rev/var.hpp>
#include <stan/agrad/rev/op/v_vari.hpp>

namespace stan {
  namespace agrad {
    
    namespace {
      class atan_vari : public op_v_vari {
      public:
        atan_vari(vari* avi) :
          op_v_vari(std::atan(avi->val_),avi) {
        }
        void chain() {
          avi_->adj_ += adj_ / (1.0 + (avi_->val_ * avi_->val_));
        }
      };
    }

    inline var atan(const var& a) {
      return var(new atan_vari(a.vi_));
    }

  }
}
#endif