lmgamma.hpp

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#ifndef STAN_MATH_REV_FUN_LMGAMMA_HPP
#define STAN_MATH_REV_FUN_LMGAMMA_HPP
 
#include <stan/math/rev/meta.hpp>
#include <stan/math/rev/core.hpp>
#include <stan/math/prim/fun/lmgamma.hpp>
#include <stan/math/prim/fun/digamma.hpp>
 
namespace stan {
namespace math {
 
namespace internal {
class lmgamma_dv_vari : public op_dv_vari {
 public:
  lmgamma_dv_vari(int a, vari* bvi)
      : op_dv_vari(lmgamma(a, bvi->val_), a, bvi) {}
  void chain() {
    double deriv = 0;
    for (int i = 1; i < ad_ + 1; i++) {
      deriv += digamma(bvi_->val_ + (1.0 - i) / 2.0);
    }
    bvi_->adj_ += adj_ * deriv;
  }
};
}  // namespace internal
 
inline var lmgamma(int a, const var& b) {
  return var(new internal::lmgamma_dv_vari(a, b.vi_));
}
 
}  // namespace math
}  // namespace stan
#endif