From 2f42af629b464da42ab78303cee203299b85f636 Mon Sep 17 00:00:00 2001
From: Kallinteris Andreas
 <30759571+Kallinteris-Andreas@users.noreply.github.com>
Date: Tue, 21 Feb 2023 19:18:16 +0200
Subject: [PATCH] `MuJoCo/Ant` clarify the lack of `use_contact_forces` on  v3
 (and older) (#342)

---
 gymnasium/envs/mujoco/ant_v4.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/gymnasium/envs/mujoco/ant_v4.py b/gymnasium/envs/mujoco/ant_v4.py
index bfb2290e5..8c0c5676b 100644
--- a/gymnasium/envs/mujoco/ant_v4.py
+++ b/gymnasium/envs/mujoco/ant_v4.py
@@ -84,7 +84,7 @@ class AntEnv(MujocoEnv, utils.EzPickle):
     | 26  |angular velocity of the angle between back right links        | -Inf   | Inf    | ankle_4 (right_back_leg)               | hinge | angle (rad)              |
 
 
-    If `use_contact_forces` is `True` then the observation space is extended by 14*6 = 84 elements, which are contact forces
+    If version < `v4` or `use_contact_forces` is `True` then the observation space is extended by 14*6 = 84 elements, which are contact forces
     (external forces - force x, y, z and torque x, y, z) applied to the
     center of mass of each of the links. The 14 links are: the ground link,
     the torso link, and 3 links for each leg (1 + 1 + 12) with the 6 external forces.
@@ -116,7 +116,7 @@ class AntEnv(MujocoEnv, utils.EzPickle):
 
     The total reward returned is ***reward*** *=* *healthy_reward + forward_reward - ctrl_cost*.
 
-    But if `use_contact_forces=True`
+    But if `use_contact_forces=True` or version < `v4`
     The total reward returned is ***reward*** *=* *healthy_reward + forward_reward - ctrl_cost - contact_cost*.
 
     In either case `info` will also contain the individual reward terms.