sqrt.hpp

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#ifndef STAN_MATH_REV_FUN_SQRT_HPP
#define STAN_MATH_REV_FUN_SQRT_HPP
 
#include <stan/math/rev/meta.hpp>
#include <stan/math/rev/core.hpp>
#include <stan/math/rev/fun/atan2.hpp>
#include <stan/math/rev/fun/cos.hpp>
#include <stan/math/rev/fun/hypot.hpp>
#include <stan/math/rev/fun/sin.hpp>
#include <stan/math/prim/fun/sqrt.hpp>
#include <cmath>
#include <complex>
 
namespace stan {
namespace math {
 
inline var sqrt(const var& a) {
  return make_callback_var(std::sqrt(a.val()), [a](auto& vi) mutable {
    if (vi.val() != 0.0) {
      a.adj() += vi.adj() / (2.0 * vi.val());
    }
  });
}
 
template <typename T, require_var_matrix_t<T>* = nullptr>
inline auto sqrt(const T& a) {
  return make_callback_var(
      a.val().array().sqrt().matrix(), [a](auto& vi) mutable {
        a.adj().array()
            += (vi.val_op().array() == 0.0)
                   .select(0.0, vi.adj().array() / (2.0 * vi.val_op().array()));
      });
}
 
inline std::complex<var> sqrt(const std::complex<var>& z) {
  return internal::complex_sqrt(z);
}
 
}  // namespace math
}  // namespace stan
#endif