sd.hpp

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#ifndef STAN_MATH_PRIM_FUN_SD_HPP
#define STAN_MATH_PRIM_FUN_SD_HPP
 
#include <stan/math/prim/err.hpp>
#include <stan/math/prim/fun/Eigen.hpp>
#include <stan/math/prim/fun/variance.hpp>
#include <stan/math/prim/fun/sqrt.hpp>
#include <vector>
#include <cmath>
 
namespace stan {
namespace math {
 
template <typename T, require_container_t<T>* = nullptr,
          require_not_st_var<T>* = nullptr>
inline auto sd(const T& m) {
  using std::sqrt;
 
  return apply_vector_unary<T>::reduce(m, [](const auto& x) {
    check_nonzero_size("sd", "x", x);
 
    if (x.size() == 1) {
      return scalar_type_t<T>(0.0);
    }
 
    return sqrt(variance(x));
  });
}
 
}  // namespace math
}  // namespace stan
 
#endif