is_unit_vector.hpp

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#ifndef STAN_MATH_PRIM_ERR_IS_UNIT_VECTOR_HPP
#define STAN_MATH_PRIM_ERR_IS_UNIT_VECTOR_HPP
 
#include <stan/math/prim/fun/Eigen.hpp>
#include <stan/math/prim/meta.hpp>
#include <stan/math/prim/err/is_nonzero_size.hpp>
#include <stan/math/prim/err/constraint_tolerance.hpp>
#include <stan/math/prim/fun/fabs.hpp>
#include <cmath>
 
namespace stan {
namespace math {
template <typename EigVec, require_eigen_vector_t<EigVec>* = nullptr>
inline bool is_unit_vector(const EigVec& theta) {
  using std::fabs;
  if (is_nonzero_size(theta)) {
    value_type_t<EigVec> seq = theta.squaredNorm();
    return fabs(1.0 - seq) <= CONSTRAINT_TOLERANCE;
  }
  return false;
}
 
}  // namespace math
}  // namespace stan
#endif