Merge pull request #3338 from stan-dev/eigen-compat

Enable backwards-compatibility with Eigen < 5

Author: andrjohns

stan/math/fwd/fun/Eigen_NumTraits.hpp

@@ -218,6 +218,7 @@ struct ScalarBinaryOpTraits<std::complex<stan::math::fvar<T>>,
 
 namespace internal {
 
+#if EIGEN_VERSION_AT_LEAST(5, 0, 0)
 /**
  * Partial specialization of Eigen's ternary evaluator for `.select()`
  * expressions on matrices of `fvar<T>`, restoring the lazy (Eigen 3.x)
@@ -247,6 +248,7 @@ struct ternary_evaluator<
       Arg1, Arg2, Arg3>;
   using Base::Base;
 };
+#endif
 
 }  // namespace internal
 

stan/math/prim/meta/lazy_select_evaluator.hpp

@@ -71,11 +71,10 @@ struct lazy_select_evaluator
                    & static_cast<int>(Arg3Flags)
                    & (StorageOrdersAgree ? Eigen::LinearAccessBit : 0))),
     Flags = (Flags0 & ~Eigen::RowMajorBit) | (Arg1Flags & Eigen::RowMajorBit),
-    Alignment = Eigen::internal::plain_enum_min(
-        Eigen::internal::plain_enum_min(
-            Eigen::internal::evaluator<Arg1>::Alignment,
-            Eigen::internal::evaluator<Arg2>::Alignment),
-        Eigen::internal::evaluator<Arg3>::Alignment)
+    Alignment
+    = std::min({static_cast<int>(Eigen::internal::evaluator<Arg1>::Alignment),
+                static_cast<int>(Eigen::internal::evaluator<Arg2>::Alignment),
+                static_cast<int>(Eigen::internal::evaluator<Arg3>::Alignment)})
   };
 
   EIGEN_DEVICE_FUNC explicit lazy_select_evaluator(const XprType& xpr)

stan/math/rev/core/Eigen_NumTraits.hpp

@@ -269,6 +269,7 @@ struct ScalarBinaryOpTraits<std::complex<stan::math::var>,
 
 namespace internal {
 
+#if EIGEN_VERSION_AT_LEAST(5, 0, 0)
 /**
  * Partial specialization of Eigen's ternary evaluator for `.select()`
  * expressions on matrices of `var`, restoring the lazy (Eigen 3.x)
@@ -299,6 +300,7 @@ struct ternary_evaluator<
       Arg1, Arg2, Arg3>;
   using Base::Base;
 };
+#endif
 
 /**
  * Enable linear access of inputs when using read_vi_val_adj.