fabs.hpp

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#ifndef STAN_MATH_REV_FUN_FABS_HPP
#define STAN_MATH_REV_FUN_FABS_HPP
 
#include <stan/math/rev/meta.hpp>
#include <stan/math/rev/core.hpp>
#include <stan/math/prim/fun/constants.hpp>
 
namespace stan {
namespace math {
 
inline var fabs(const var& a) {
  if (a.val() > 0.0) {
    return a;
  } else if (a.val() < 0.0) {
    return -a;
  } else if (a.val() == 0) {
    return var(new vari(0));
  } else {
    return make_callback_var(NOT_A_NUMBER,
                             [a](auto& vi) mutable { a.adj() = NOT_A_NUMBER; });
  }
}
 
template <typename VarMat, require_var_matrix_t<VarMat>* = nullptr>
inline auto fabs(const VarMat& a) {
  return make_callback_var(
      a.val().unaryExpr([](const auto x) {
        if (unlikely(is_nan(x))) {
          return NOT_A_NUMBER;
        } else {
          return std::abs(x);
        }
      }),
      [a](const auto& vi) mutable {
        for (Eigen::Index j = 0; j < vi.cols(); ++j) {
          for (Eigen::Index i = 0; i < vi.rows(); ++i) {
            const auto x = a.val().coeffRef(i, j);
            if (unlikely(is_nan(x))) {
              a.adj().coeffRef(i, j) = NOT_A_NUMBER;
            } else if (x < 0.0) {
              a.adj().coeffRef(i, j) -= vi.adj_.coeff(i, j);
            } else {
              a.adj().coeffRef(i, j) += vi.adj_.coeff(i, j);
            }
          }
        }
      });
}
 
}  // namespace math
}  // namespace stan
#endif