Merge pull request #3228 from stan-dev/fix/exprs-apply

update bessel so that reverse mode is chosen over the perfect forward…

Author: WardBrian

stan/math/prim/fun/bessel_second_kind.hpp

@@ -52,7 +52,8 @@ inline T2 bessel_second_kind(int v, const T2 z) {
  * @param b Second input
  * @return Bessel second kind function applied to the two inputs.
  */
-template <typename T1, typename T2, require_any_container_t<T1, T2>* = nullptr>
+template <typename T1, typename T2, require_any_container_t<T1, T2>* = nullptr,
+          require_not_var_matrix_t<T2>* = nullptr>
 inline auto bessel_second_kind(T1&& a, T2&& b) {
   return apply_scalar_binary(
       [](auto&& c, auto&& d) {

stan/math/prim/functor/apply_scalar_unary.hpp

@@ -4,6 +4,7 @@
 #include <stan/math/prim/fun/Eigen.hpp>
 #include <stan/math/prim/meta/is_eigen.hpp>
 #include <stan/math/prim/meta/is_complex.hpp>
+#include <stan/math/prim/meta/holder.hpp>
 #include <stan/math/prim/meta/require_generics.hpp>
 #include <stan/math/prim/meta/is_vector.hpp>
 #include <stan/math/prim/meta/is_vector_like.hpp>

stan/math/rev/fun/bessel_second_kind.hpp

@@ -8,7 +8,9 @@
 namespace stan {
 namespace math {
 
-inline var bessel_second_kind(int v, const var& a) {
+template <typename T1, typename T2, require_integral_t<T1>* = nullptr,
+          require_var_t<T2>* = nullptr, require_stan_scalar_t<T2>* = nullptr>
+inline var bessel_second_kind(T1&& v, T2&& a) {
   double ret_val = bessel_second_kind(v, a.val());
   auto precomp_bessel
       = v * ret_val / a.val() - bessel_second_kind(v + 1, a.val());
@@ -22,8 +24,8 @@ inline var bessel_second_kind(int v, const var& a) {
  * `std::vector<std::vector<int>>`
  */
 template <typename T1, typename T2, require_st_integral<T1>* = nullptr,
-          require_eigen_t<T2>* = nullptr>
-inline auto bessel_second_kind(const T1& v, const var_value<T2>& a) {
+          require_var_matrix_t<T2>* = nullptr>
+inline auto bessel_second_kind(T1&& v, T2&& a) {
   auto ret_val = bessel_second_kind(v, a.val()).array().eval();
   auto v_map = as_array_or_scalar(v);
   auto precomp_bessel

test/unit/math/mix/fun/bessel_second_kind_test.cpp

@@ -3,7 +3,7 @@
 
 TEST(mathMixScalFun, besselSecondKind) {
   // bind integer arg because can't autodiff through
-  auto f = [](const int x1) {
+  auto f = [](const auto& x1) {
     return
         [=](const auto& x2) { return stan::math::bessel_second_kind(x1, x2); };
   };
@@ -13,6 +13,13 @@ TEST(mathMixScalFun, besselSecondKind) {
   stan::test::expect_ad(f(1), 3.0);
   stan::test::expect_ad(f(1), std::numeric_limits<double>::quiet_NaN());
   stan::test::expect_ad(f(2), 2.79);
+  std::vector<int> std_in1{3, 1};
+  stan::test::expect_ad(f(std_in1), 4.0);
+  stan::test::expect_ad(f(std_in1), std::numeric_limits<double>::quiet_NaN());
+  stan::test::expect_ad(f(std_in1), -3.0);
+  stan::test::expect_ad(f(std_in1), 3.0);
+  stan::test::expect_ad(f(std_in1), std::numeric_limits<double>::quiet_NaN());
+  stan::test::expect_ad(f(std_in1), 2.79);
 }
 
 TEST(mathMixScalFun, besselSecondKind_vec) {
@@ -25,10 +32,12 @@ TEST(mathMixScalFun, besselSecondKind_vec) {
   Eigen::VectorXd in2(2);
   in2 << 0.5, 3.4;
   stan::test::expect_ad_vectorized_binary(f, std_in1, in2);
+  stan::test::expect_ad_matvar(f, std_in1, in2);
 
   std::vector<std::vector<int>> std_std_in1{std_in1, std_in1};
   Eigen::MatrixXd mat_in2 = in2.replicate(1, 2);
   stan::test::expect_ad_vectorized_binary(f, std_std_in1, mat_in2);
+  stan::test::expect_ad_matvar(f, std_std_in1, mat_in2);
 }
 
 TEST(mathMixScalFun, besselSecondKind_matvec) {