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unit_vector_free.hpp
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1 #ifndef STAN_MATH_PRIM_MAT_FUN_UNIT_VECTOR_FREE_HPP
2 #define STAN_MATH_PRIM_MAT_FUN_UNIT_VECTOR_FREE_HPP
3
4 #include <stan/math/prim/mat/fun/Eigen.hpp>
5 #include <stan/math/prim/mat/meta/index_type.hpp>
6 #include <stan/math/prim/mat/err/check_unit_vector.hpp>
7 #include <cmath>
8
9 namespace stan {
10
11 namespace math {
12
13
14 template <typename T>
15 Eigen::Matrix<T, Eigen::Dynamic, 1>
16 unit_vector_free(const Eigen::Matrix<T, Eigen::Dynamic, 1>& x) {
17 using Eigen::Matrix;
18 using Eigen::Dynamic;
19
20 stan::math::check_unit_vector("stan::math::unit_vector_free",
21 "Unit vector variable", x);
22 int Km1 = x.size() - 1;
23 Matrix<T, Dynamic, 1> y(Km1);
24 T sumSq = x(Km1)*x(Km1);
25 const T half_pi = T(M_PI/2.0);
26 for (int k = Km1; --k >= 0; ) {
27 y(k) = atan2(sqrt(sumSq), x(k)) - half_pi;
28 sumSq += x(k)*x(k);
29 }
30 return y;
31 }
32
33 }
34
35 }
36
37 #endif
stan::math::sqrt
fvar< T > sqrt(const fvar< T > &x)
Definition: sqrt.hpp:15
stan::math::atan2
fvar< T > atan2(const fvar< T > &x1, const fvar< T > &x2)
Definition: atan2.hpp:12
stan::math::check_unit_vector
bool check_unit_vector(const char *function, const char *name, const Eigen::Matrix< T_prob, Dynamic, 1 > &theta)
Return true if the specified vector is unit vector.
Definition: check_unit_vector.hpp:38
check_unit_vector.hpp
index_type.hpp
stan::math::unit_vector_free
Eigen::Matrix< T, Eigen::Dynamic, 1 > unit_vector_free(const Eigen::Matrix< T, Eigen::Dynamic, 1 > &x)
Definition: unit_vector_free.hpp:16
Eigen.hpp

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