Merge pull request #2840 from stan-dev/feature/vectorize-minus

Allow stan::math::minus on std::vectors

Author: WardBrian

stan/math/prim/fun/minus.hpp

@@ -2,6 +2,7 @@
 #define STAN_MATH_PRIM_FUN_MINUS_HPP
 
 #include <stan/math/prim/meta.hpp>
+#include <stan/math/prim/functor/apply_vector_unary.hpp>
 
 namespace stan {
 namespace math {
@@ -13,11 +14,24 @@ namespace math {
  * @param x Subtrahend.
  * @return Negation of subtrahend.
  */
-template <typename T>
+template <typename T, require_not_std_vector_t<T>* = nullptr>
 inline auto minus(const T& x) {
   return -x;
 }
 
+/**
+ * Return the negation of the each element of a vector
+ *
+ * @tparam T Type of container.
+ * @param x Container.
+ * @return Container where each element is negated.
+ */
+template <typename T>
+inline auto minus(const std::vector<T>& x) {
+  return apply_vector_unary<std::vector<T>>::apply(
+      x, [](const auto& v) { return -v; });
+}
+
 }  // namespace math
 }  // namespace stan
 

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

@@ -39,4 +39,9 @@ TEST(MathMixMatFun, minus) {
   for (const auto& y : std::vector<Eigen::MatrixXd>{u00, u11, u22, u23}) {
     stan::test::expect_ad(f, y);
   }
+
+  Eigen::MatrixXd v22(2, 2);
+  v22 << 5, 6, 7, 8;
+  std::vector<Eigen::MatrixXd> vec_mat{u22, v22};
+  stan::test::expect_ad(f, vec_mat);
 }

test/unit/math/prim/fun/minus_test.cpp

@@ -10,3 +10,9 @@ TEST(MathMatrixPrimMat, minus) {
   EXPECT_EQ(0, stan::math::minus(rv0).size());
   EXPECT_EQ(0, stan::math::minus(m0).size());
 }
+
+TEST(MathMatrixPrimMat, vectorized_minus) {
+  // test int->int
+  std::vector<int> u{1, 2, 3, 4};
+  std::vector<int> v = stan::math::minus(u);
+}