Merge pull request #3214 from stan-dev/eigen-custom-assert-better

Include assertion that failed in STAN_OVERRIDE_EIGEN_ASSERT

Author: WardBrian

stan/math/prim/fun/Eigen.hpp

@@ -5,9 +5,10 @@
 #ifdef eigen_assert
 #undef eigen_assert
 #endif
-#define eigen_assert(x)                               \
-  if (!(x)) {                                         \
-    throw(std::domain_error("Internal Eigen Error")); \
+#define eigen_assert(x)                                            \
+  if (!(x)) {                                                      \
+    throw(std::domain_error("Internal Eigen Error: Assertion '" #x \
+                            "' failed in " __FILE__));             \
   }
 #endif
 #ifdef EIGEN_MATRIXBASE_PLUGIN