adds tests for x + x.transpose

Author: SteveBronder

test/unit/math/mix/core/operator_addition_test.cpp

@@ -139,3 +139,18 @@ TEST(mathMixCore, operatorAdditionMatrixFailures) {
   stan::test::expect_ad_matvar(tols, f, u, vv);
   stan::test::expect_ad_matvar(tols, f, rvv, u);
 }
+TEST(mathMixCore, operatorAdditionMatrixLinearAccess) {
+  Eigen::MatrixXd matrix_m11(3, 3);
+  for (Eigen::Index i = 0; i < matrix_m11.size(); ++i) {
+    matrix_m11(i) = i;
+  }
+  stan::math::var_value<Eigen::MatrixXd> A(matrix_m11);
+  stan::math::var_value<Eigen::MatrixXd> B = stan::math::add(A, A.transpose());
+  B.adj()(2, 0) = 1;
+  stan::math::grad();
+  Eigen::MatrixXd expected_adj = Eigen::MatrixXd::Zero(3, 3);
+  expected_adj(2, 0) = 1;
+  expected_adj(0, 2) = 1;
+  EXPECT_MATRIX_FLOAT_EQ(A.adj(), expected_adj);
+  stan::math::recover_memory();
+}

test/unit/math/mix/core/operator_subtraction_test.cpp

@@ -143,3 +143,20 @@ TEST(mathMixCore, operatorSubtractionMatrixFailures) {
   stan::test::expect_ad_matvar(tols, f, u, vv);
   stan::test::expect_ad_matvar(tols, f, rvv, u);
 }
+
+
+TEST(mathMixCore, operatorSubtractionMatrixLinearAccess) {
+  Eigen::MatrixXd matrix_m11(3, 3);
+  for (Eigen::Index i = 0; i < matrix_m11.size(); ++i) {
+    matrix_m11(i) = i;
+  }
+  stan::math::var_value<Eigen::MatrixXd> A(matrix_m11);
+  stan::math::var_value<Eigen::MatrixXd> B = stan::math::subtract(A, A.transpose());
+  B.adj()(2, 0) = 1;
+  stan::math::grad();
+  Eigen::MatrixXd expected_adj = Eigen::MatrixXd::Zero(3, 3);
+  expected_adj(2, 0) = 1;
+  expected_adj(0, 2) = -1;
+  EXPECT_MATRIX_FLOAT_EQ(A.adj(), expected_adj);
+  stan::math::recover_memory();
+}