Alway use CwiseUnaryOp for .val() of var types

doxygen/contributor_help_pages/getting_started.md

@@ -660,9 +660,15 @@ The values of `x` have the same shape as `x`.
 
 ### Values and adjoint extensions to Eigen
 
-The matrix and vector autodiff types come with an extra `.val()` and `.adj()`, member functions called `.val_op()` and `.adj_op()`.
-These `*_op()` member functions are used as a workaround for a bug in Eigen where transpose expressions will be inaccessible because of an incorrect const reference.
-See [here](https://github.com/stan-dev/math/issues/2653) for the details and other information for when this workaround is needed.
+By default, `.val()` and `.adj()` return a `CwiseUnaryView` when the matrix/vector is non-`const`,
+and returns a `CwiseUnaryOp` when the matrix/vector is `const`. The exception is that
+calling `.val()` on a matrix/vector of `var` types will always return a `CwiseUnaryOp`, as the
+underlying value is always `const`.
+
+However, using a `CwiseUnaryView` in some Eigen operations (e.g., multiplication, transposition)
+can result in a compilation error. To workaround this, the `.val_op()` and `.adj_op()` member
+functions have been added to explicitly request a `CwiseUnaryOp` regardless of whether the
+matrix/vector is `const` or not.
 
 The member functions `.val()` and `.val_op()` return expressions that evaluate to the values
 of the autodiff matrix.

stan/math/prim/eigen_plugins.h

@@ -82,6 +82,7 @@ struct val_Op{
   double& operator()(double& v) const { return v; }
 };
 
+
 /**
  * Coefficient-wise function applying val_Op struct to a matrix of const var
  * or vari* and returning a view to the const matrix of doubles containing
@@ -94,16 +95,31 @@ val() const { return CwiseUnaryOp<val_Op, const Derived>(derived());
 /**
  * Coefficient-wise function applying val_Op struct to a matrix of var
  * or vari* and returning a view to the values
- */
+ */ 
+template <
+  typename T = Scalar,
+  std::enable_if_t<
+    !std::disjunction_v<
+      std::is_arithmetic<std::decay_t<T>>,
+      is_fvar<std::decay_t<T>>
+    >
+  >* = nullptr>
+inline CwiseUnaryOp<val_Op, Derived>
+val() { return CwiseUnaryOp<val_Op, Derived>(derived());
+}
+
+template <
+  typename T = Scalar,
+  std::enable_if_t<
+    std::disjunction_v<
+      std::is_arithmetic<std::decay_t<T>>,
+      is_fvar<std::decay_t<T>>
+    >
+  >* = nullptr>
 inline CwiseUnaryView<val_Op, Derived>
 val() { return CwiseUnaryView<val_Op, Derived>(derived());
 }
 
-/**
- * Coefficient-wise function applying val_Op struct to a matrix of var
- * or vari* and returning a view to the matrix of doubles containing
- * the values
- */
 inline CwiseUnaryOp<val_Op, Derived>
 val_op() { return CwiseUnaryOp<val_Op, Derived>(derived());
 }

stan/math/rev/constraint/stochastic_column_constrain.hpp

@@ -30,7 +30,7 @@ inline plain_type_t<T> stochastic_column_constrain(const T& y) {
   const auto M = y.cols();
   arena_t<T> arena_y = y;
 
-  arena_t<ret_type> arena_x = stochastic_column_constrain(arena_y.val_op());
+  arena_t<ret_type> arena_x = stochastic_column_constrain(arena_y.val());
 
   if (unlikely(N == 0 || M == 0)) {
     return arena_x;
@@ -39,7 +39,7 @@ inline plain_type_t<T> stochastic_column_constrain(const T& y) {
   reverse_pass_callback([arena_y, arena_x]() mutable {
     const auto M = arena_y.cols();
 
-    auto&& x_val = arena_x.val_op();
+    auto&& x_val = arena_x.val();
     auto&& x_adj = arena_x.adj_op();
 
     Eigen::VectorXd x_pre_softmax_adj(x_val.rows());
@@ -82,7 +82,7 @@ inline plain_type_t<T> stochastic_column_constrain(const T& y,
 
   double lp_val = 0;
   arena_t<ret_type> arena_x
-      = stochastic_column_constrain(arena_y.val_op(), lp_val);
+      = stochastic_column_constrain(arena_y.val(), lp_val);
   lp += lp_val;
 
   if (unlikely(N == 0 || M == 0)) {
@@ -92,7 +92,7 @@ inline plain_type_t<T> stochastic_column_constrain(const T& y,
   reverse_pass_callback([arena_y, arena_x, lp]() mutable {
     const auto M = arena_y.cols();
 
-    auto&& x_val = arena_x.val_op();
+    auto&& x_val = arena_x.val();
     auto&& x_adj = arena_x.adj_op();
 
     const auto x_val_rows = x_val.rows();

stan/math/rev/constraint/stochastic_row_constrain.hpp

@@ -28,7 +28,7 @@ inline auto stochastic_row_constrain(const T& y) {
   const auto M = y.cols();
   arena_t<T> arena_y = y;
 
-  arena_t<ret_type> arena_x = stochastic_row_constrain(arena_y.val_op());
+  arena_t<ret_type> arena_x = stochastic_row_constrain(arena_y.val());
 
   if (unlikely(N == 0 || M == 0)) {
     return arena_x;
@@ -37,7 +37,7 @@ inline auto stochastic_row_constrain(const T& y) {
   reverse_pass_callback([arena_y, arena_x]() mutable {
     const auto N = arena_y.rows();
 
-    auto&& x_val = arena_x.val_op();
+    auto&& x_val = arena_x.val();
     auto&& x_adj = arena_x.adj_op();
 
     Eigen::VectorXd x_pre_softmax_adj(x_val.cols());
@@ -79,8 +79,7 @@ inline plain_type_t<T> stochastic_row_constrain(const T& y,
   arena_t<T> arena_y = y;
 
   double lp_val = 0;
-  arena_t<ret_type> arena_x
-      = stochastic_row_constrain(arena_y.val_op(), lp_val);
+  arena_t<ret_type> arena_x = stochastic_row_constrain(arena_y.val(), lp_val);
   lp += lp_val;
 
   if (unlikely(N == 0 || M == 0)) {
@@ -90,7 +89,7 @@ inline plain_type_t<T> stochastic_row_constrain(const T& y,
   reverse_pass_callback([arena_y, arena_x, lp]() mutable {
     const auto N = arena_y.rows();
 
-    auto&& x_val = arena_x.val_op();
+    auto&& x_val = arena_x.val();
     auto&& x_adj = arena_x.adj_op();
 
     const auto x_val_cols = x_val.cols();

stan/math/rev/fun/eigendecompose_sym.hpp

@@ -41,20 +41,19 @@ inline auto eigendecompose_sym(const T& m) {
 
   reverse_pass_callback([eigenvals, arena_m, eigenvecs]() mutable {
     // eigenvalue reverse calculation
-    auto value_adj = eigenvecs.val_op() * eigenvals.adj().asDiagonal()
-                     * eigenvecs.val_op().transpose();
+    auto value_adj = eigenvecs.val() * eigenvals.adj().asDiagonal()
+                     * eigenvecs.val().transpose();
     // eigenvector reverse calculation
     const auto p = arena_m.val().cols();
-    Eigen::MatrixXd f
-        = (1
-           / (eigenvals.val_op().rowwise().replicate(p).transpose()
-              - eigenvals.val_op().rowwise().replicate(p))
-                 .array());
+    Eigen::MatrixXd f = (1
+                         / (eigenvals.val().rowwise().replicate(p).transpose()
+                            - eigenvals.val().rowwise().replicate(p))
+                               .array());
     f.diagonal().setZero();
     auto vector_adj
-        = eigenvecs.val_op()
-          * f.cwiseProduct(eigenvecs.val_op().transpose() * eigenvecs.adj_op())
-          * eigenvecs.val_op().transpose();
+        = eigenvecs.val()
+          * f.cwiseProduct(eigenvecs.val().transpose() * eigenvecs.adj_op())
+          * eigenvecs.val().transpose();
 
     arena_m.adj() += value_adj + vector_adj;
   });

stan/math/rev/fun/eigenvectors_sym.hpp

@@ -43,9 +43,9 @@ inline auto eigenvectors_sym(const T& m) {
                                .array());
     f.diagonal().setZero();
     arena_m.adj()
-        += eigenvecs.val_op()
-           * f.cwiseProduct(eigenvecs.val_op().transpose() * eigenvecs.adj_op())
-           * eigenvecs.val_op().transpose();
+        += eigenvecs.val()
+           * f.cwiseProduct(eigenvecs.val().transpose() * eigenvecs.adj_op())
+           * eigenvecs.val().transpose();
   });
 
   return return_t(eigenvecs);

stan/math/rev/fun/generalized_inverse.hpp

@@ -24,15 +24,13 @@ template <typename T1, typename T2>
 inline auto generalized_inverse_lambda(T1& G_arena, T2& inv_G) {
   return [G_arena, inv_G]() mutable {
     G_arena.adj()
-        += -(inv_G.val_op().transpose() * inv_G.adj_op()
-             * inv_G.val_op().transpose())
-           + (-G_arena.val_op() * inv_G.val_op()
+        += -(inv_G.val().transpose() * inv_G.adj_op() * inv_G.val().transpose())
+           + (-G_arena.val() * inv_G.val()
               + Eigen::MatrixXd::Identity(G_arena.rows(), inv_G.cols()))
-                 * inv_G.adj_op().transpose() * inv_G.val_op()
-                 * inv_G.val_op().transpose()
-           + inv_G.val_op().transpose() * inv_G.val_op()
-                 * inv_G.adj_op().transpose()
-                 * (-inv_G.val_op() * G_arena.val_op()
+                 * inv_G.adj_op().transpose() * inv_G.val()
+                 * inv_G.val().transpose()
+           + inv_G.val().transpose() * inv_G.val() * inv_G.adj_op().transpose()
+                 * (-inv_G.val() * G_arena.val()
                     + Eigen::MatrixXd::Identity(inv_G.rows(), G_arena.cols()));
   };
 }
@@ -83,17 +81,17 @@ inline auto generalized_inverse(const VarMat& G) {
     }
   } else if (G.rows() < G.cols()) {
     arena_t<VarMat> G_arena(G);
-    arena_t<ret_type> inv_G((G_arena.val_op() * G_arena.val_op().transpose())
+    arena_t<ret_type> inv_G((G_arena.val() * G_arena.val().transpose())
                                 .ldlt()
-                                .solve(G_arena.val_op())
+                                .solve(G_arena.val())
                                 .transpose());
     reverse_pass_callback(internal::generalized_inverse_lambda(G_arena, inv_G));
     return ret_type(inv_G);
   } else {
     arena_t<VarMat> G_arena(G);
-    arena_t<ret_type> inv_G((G_arena.val_op().transpose() * G_arena.val_op())
+    arena_t<ret_type> inv_G((G_arena.val().transpose() * G_arena.val())
                                 .ldlt()
-                                .solve(G_arena.val_op().transpose()));
+                                .solve(G_arena.val().transpose()));
     reverse_pass_callback(internal::generalized_inverse_lambda(G_arena, inv_G));
     return ret_type(inv_G);
   }

stan/math/rev/fun/inverse.hpp

@@ -30,7 +30,7 @@ inline auto inverse(const T& m) {
   }
 
   arena_t<T> arena_m = m;
-  arena_t<promote_scalar_t<double, T>> res_val = arena_m.val_op().inverse();
+  arena_t<promote_scalar_t<double, T>> res_val = arena_m.val().inverse();
   arena_t<ret_type> res = res_val;
 
   reverse_pass_callback([res, res_val, arena_m]() mutable {

stan/math/rev/fun/mdivide_left.hpp

@@ -42,24 +42,24 @@ inline auto mdivide_left(T1&& A, T2&& B) {
   if constexpr (is_autodiff_v<T1> && is_autodiff_v<T2>) {
     arena_t<T1> arena_A(std::forward<T1>(A));
     arena_t<T2> arena_B(std::forward<T2>(B));
-    auto hqr_A_ptr = make_chainable_ptr(arena_A.val_op().householderQr());
-    arena_t<ret_type> res = hqr_A_ptr->solve(arena_B.val_op());
+    auto hqr_A_ptr = make_chainable_ptr(arena_A.val().householderQr());
+    arena_t<ret_type> res = hqr_A_ptr->solve(arena_B.val());
     reverse_pass_callback([arena_A, arena_B, hqr_A_ptr, res]() mutable {
       promote_scalar_t<double, T2> adjB
           = hqr_A_ptr->householderQ()
             * hqr_A_ptr->matrixQR()
                   .template triangularView<Eigen::Upper>()
                   .transpose()
                   .solve(res.adj());
-      arena_A.adj() -= adjB * res.val_op().transpose();
+      arena_A.adj() -= adjB * res.val().transpose();
       arena_B.adj() += adjB;
     });
 
     return ret_type(res);
   } else if constexpr (is_autodiff_v<T2>) {
     arena_t<T2> arena_B(std::forward<T2>(B));
     auto hqr_A_ptr = make_chainable_ptr(value_of(A).householderQr());
-    arena_t<ret_type> res = hqr_A_ptr->solve(arena_B.val_op());
+    arena_t<ret_type> res = hqr_A_ptr->solve(arena_B.val());
     reverse_pass_callback([arena_B, hqr_A_ptr, res]() mutable {
       arena_B.adj() += hqr_A_ptr->householderQ()
                        * hqr_A_ptr->matrixQR()
@@ -70,15 +70,15 @@ inline auto mdivide_left(T1&& A, T2&& B) {
     return ret_type(res);
   } else {
     arena_t<T1> arena_A(std::forward<T1>(A));
-    auto hqr_A_ptr = make_chainable_ptr(arena_A.val_op().householderQr());
+    auto hqr_A_ptr = make_chainable_ptr(arena_A.val().householderQr());
     arena_t<ret_type> res = hqr_A_ptr->solve(value_of(B));
     reverse_pass_callback([arena_A, hqr_A_ptr, res]() mutable {
       arena_A.adj() -= hqr_A_ptr->householderQ()
                        * hqr_A_ptr->matrixQR()
                              .template triangularView<Eigen::Upper>()
                              .transpose()
                              .solve(res.adj())
-                       * res.val_op().transpose();
+                       * res.val().transpose();
     });
     return ret_type(res);
   }

stan/math/rev/fun/mdivide_left_ldlt.hpp

@@ -39,13 +39,13 @@ inline auto mdivide_left_ldlt(LDLT_factor<T1>& A, const T2& B) {
   if constexpr (is_autodiff_v<T1> && is_autodiff_v<T2>) {
     arena_t<promote_scalar_t<var, T2>> arena_B = B;
     arena_t<promote_scalar_t<var, T1>> arena_A = A.matrix();
-    arena_t<ret_type> res = A.ldlt().solve(arena_B.val_op());
+    arena_t<ret_type> res = A.ldlt().solve(arena_B.val());
     const auto* ldlt_ptr = make_chainable_ptr(A.ldlt());
 
     reverse_pass_callback([arena_A, arena_B, ldlt_ptr, res]() mutable {
       promote_scalar_t<double, T2> adjB = ldlt_ptr->solve(res.adj());
 
-      arena_A.adj() -= adjB * res.val_op().transpose();
+      arena_A.adj() -= adjB * res.val().transpose();
       arena_B.adj() += adjB;
     });
 
@@ -56,13 +56,13 @@ inline auto mdivide_left_ldlt(LDLT_factor<T1>& A, const T2& B) {
     const auto* ldlt_ptr = make_chainable_ptr(A.ldlt());
 
     reverse_pass_callback([arena_A, ldlt_ptr, res]() mutable {
-      arena_A.adj() -= ldlt_ptr->solve(res.adj()) * res.val_op().transpose();
+      arena_A.adj() -= ldlt_ptr->solve(res.adj()) * res.val().transpose();
     });
 
     return ret_type(res);
   } else {
     arena_t<promote_scalar_t<var, T2>> arena_B = B;
-    arena_t<ret_type> res = A.ldlt().solve(arena_B.val_op());
+    arena_t<ret_type> res = A.ldlt().solve(arena_B.val());
     const auto* ldlt_ptr = make_chainable_ptr(A.ldlt());
 
     reverse_pass_callback([arena_B, ldlt_ptr, res]() mutable {

stan/math/rev/fun/mdivide_left_spd.hpp

@@ -276,12 +276,12 @@ inline auto mdivide_left_spd(const T1 &A, const T2 &B) {
     check_symmetric("mdivide_left_spd", "A", arena_A.val());
     check_not_nan("mdivide_left_spd", "A", arena_A.val());
 
-    auto A_llt = arena_A.val_op().llt();
+    auto A_llt = arena_A.val().llt();
 
     check_pos_definite("mdivide_left_spd", "A", A_llt);
 
     arena_t<Eigen::MatrixXd> arena_A_llt = A_llt.matrixL();
-    arena_t<ret_type> res = A_llt.solve(arena_B.val_op());
+    arena_t<ret_type> res = A_llt.solve(arena_B.val());
 
     reverse_pass_callback([arena_A, arena_B, arena_A_llt, res]() mutable {
       promote_scalar_t<double, T2> adjB = res.adj();
@@ -291,7 +291,7 @@ inline auto mdivide_left_spd(const T1 &A, const T2 &B) {
           .transpose()
           .solveInPlace(adjB);
 
-      arena_A.adj() -= adjB * res.val_op().transpose();
+      arena_A.adj() -= adjB * res.val().transpose();
       arena_B.adj() += adjB;
     });
 
@@ -302,7 +302,7 @@ inline auto mdivide_left_spd(const T1 &A, const T2 &B) {
     check_symmetric("mdivide_left_spd", "A", arena_A.val());
     check_not_nan("mdivide_left_spd", "A", arena_A.val());
 
-    auto A_llt = arena_A.val_op().llt();
+    auto A_llt = arena_A.val().llt();
 
     check_pos_definite("mdivide_left_spd", "A", A_llt);
 
@@ -317,7 +317,7 @@ inline auto mdivide_left_spd(const T1 &A, const T2 &B) {
           .transpose()
           .solveInPlace(adjB);
 
-      arena_A.adj() -= adjB * res.val_op().transpose().eval();
+      arena_A.adj() -= adjB * res.val().transpose().eval();
     });
 
     return ret_type(res);
@@ -333,7 +333,7 @@ inline auto mdivide_left_spd(const T1 &A, const T2 &B) {
     check_pos_definite("mdivide_left_spd", "A", A_llt);
 
     arena_t<Eigen::MatrixXd> arena_A_llt = A_llt.matrixL();
-    arena_t<ret_type> res = A_llt.solve(arena_B.val_op());
+    arena_t<ret_type> res = A_llt.solve(arena_B.val());
 
     reverse_pass_callback([arena_B, arena_A_llt, res]() mutable {
       promote_scalar_t<double, T2> adjB = res.adj();