From fc2209612eaa08b3f2de5703eb675f998cf419b0 Mon Sep 17 00:00:00 2001
From: GiovanniCanali <giovanni.canali98@yahoo.it>
Date: Mon, 23 Feb 2026 10:54:36 +0100
Subject: [PATCH] fix residual stack

---
 pina/_src/equation/system_equation.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/pina/_src/equation/system_equation.py b/pina/_src/equation/system_equation.py
index a9920a955..adaeca444 100644
--- a/pina/_src/equation/system_equation.py
+++ b/pina/_src/equation/system_equation.py
@@ -105,11 +105,12 @@ def residual(self, input_, output_, params_=None):
         self.to(input_.device)
 
         # Compute the residual for each equation
-        residual = torch.hstack(
+        residual = torch.cat(
             [
                 equation.residual(input_, output_, params_)
                 for equation in self.equations
-            ]
+            ],
+            dim=-1,
         )
 
         # Skip reduction if not specified