acos.hpp

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#ifndef __STAN__AGRAD__REV__ACOS_HPP__
#define __STAN__AGRAD__REV__ACOS_HPP__

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

namespace stan {
  namespace agrad {

    namespace {
      class acos_vari : public op_v_vari {
      public:
        acos_vari(vari* avi) :
        op_v_vari(std::acos(avi->val_),avi) {
        }
        void chain() {
          avi_->adj_ -= adj_ / std::sqrt(1.0 - (avi_->val_ * avi_->val_));
        }
      };
    }

    inline var acos(const var& a) {
      return var(new acos_vari(a.vi_));
    }

  }
}
#endif