minor polishing

Author: Jachym.Barvinek

stan/math/rev/fun/log_softmax.hpp

@@ -29,9 +29,9 @@ inline auto log_softmax(T&& x) {
       = return_var_matrix_t<plain_type_t<decltype(x_arena.val())>, T>;
   arena_t<return_t> res = log_softmax(x_arena.val());
   reverse_pass_callback([x_arena, res]() mutable {
-    const auto s = res.val().array().exp().eval();
     const auto& res_adj = to_ref(res.adj());
-    x_arena.adj().array() += res_adj.array() - res_adj.sum() * s;
+    x_arena.adj().array()
+        += res_adj.array() - res_adj.sum() * res.val().array().exp();
   });
   return return_t(res);
 }

stan/math/rev/fun/softmax.hpp

@@ -27,8 +27,7 @@ inline auto softmax(T&& x) {
   if (x_arena.size() == 0) {
     return return_t(x_arena);
   }
-  auto res_val = to_arena(softmax(x_arena.val()));
-  arena_t<return_t> res = res_val;
+  arena_t<return_t> res = softmax(x_arena.val());
   reverse_pass_callback([x_arena, res]() mutable {
     const auto& s = to_ref(res.val());
     const auto& res_adj = to_ref(res.adj());