erf.hpp

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#ifndef STAN_MATH_REV_FUN_ERF_HPP
#define STAN_MATH_REV_FUN_ERF_HPP
 
#include <stan/math/rev/meta.hpp>
#include <stan/math/rev/core.hpp>
#include <stan/math/prim/fun/constants.hpp>
#include <stan/math/prim/fun/erf.hpp>
#include <cmath>
 
namespace stan {
namespace math {
 
inline var erf(const var& a) {
  auto precomp_erf = TWO_OVER_SQRT_PI * std::exp(-a.val() * a.val());
  return make_callback_var(erf(a.val()), [a, precomp_erf](auto& vi) mutable {
    a.adj() += vi.adj() * precomp_erf;
  });
}
 
template <typename T, require_matrix_t<T>* = nullptr>
inline auto erf(const var_value<T>& a) {
  auto precomp_erf
      = to_arena(TWO_OVER_SQRT_PI * (-a.val().array().square()).exp());
  return make_callback_var(erf(a.val()), [a, precomp_erf](auto& vi) mutable {
    a.adj().array() += vi.adj().array() * precomp_erf;
  });
}
 
}  // namespace math
}  // namespace stan
#endif