erfcx.hpp

Go to the documentation of this file.

#ifndef STAN_MATH_REV_FUN_ERFCX_HPP
#define STAN_MATH_REV_FUN_ERFCX_HPP
 
#include <stan/math/rev/core.hpp>
#include <stan/math/rev/meta.hpp>
#include <stan/math/prim/fun/as_array_or_scalar.hpp>
#include <stan/math/prim/fun/constants.hpp>
#include <stan/math/prim/fun/erfcx.hpp>
#include <stan/math/prim/functor/apply_scalar_binary.hpp>
#include <cmath>
 
namespace stan {
namespace math {
 
template <
    typename T, require_var_t<T>* = nullptr,
    require_all_not_nonscalar_prim_or_rev_kernel_expression_t<T>* = nullptr>
inline auto erfcx(T&& a) {
  auto val = to_arena(erfcx(a.val()));
  return make_callback_var(val, [a, val](auto& vi) mutable {
    // apply_scalar_binary returns a lazy binaryExpr for Eigen inputs, so
    // this allocates nothing, and calls the functor directly for scalars.
    auto deriv = apply_scalar_binary(
        [](double x, double v) { return internal::erfcx_derivative(x, v); },
        a.val(), val);
    as_array_or_scalar(a.adj())
        += as_array_or_scalar(vi.adj()) * as_array_or_scalar(deriv);
  });
}
 
}  // namespace math
}  // namespace stan
#endif