From 88b4b96c6e71bf541eb9cf1724d939d6e71572da Mon Sep 17 00:00:00 2001
From: xinpw8 <scabnft@gmail.com>
Date: Fri, 9 Jan 2026 05:18:56 -0600
Subject: [PATCH] Fix cartpole standalone demo after contextualization

Commit 941198fc ("Contextualize cartpole") moved physics parameters from
#define constants to struct fields for Python configurability, but did
not update cartpole.c to initialize them. This broke the standalone demo
with division-by-zero / NaN errors.

Initialize physics parameters using designated initializers, consistent
with other ocean environments like pong.c.
---
 pufferlib/ocean/cartpole/cartpole.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/pufferlib/ocean/cartpole/cartpole.c b/pufferlib/ocean/cartpole/cartpole.c
index 20e834b37..839818a10 100644
--- a/pufferlib/ocean/cartpole/cartpole.c
+++ b/pufferlib/ocean/cartpole/cartpole.c
@@ -29,8 +29,15 @@ void demo() {
     
     int logit_sizes[1] = {ACTIONS_SIZE};
     net = make_linearlstm(weights, 1, OBSERVATIONS_SIZE, logit_sizes, 1);
-    Cartpole env = {0};
-    env.continuous = CONTINUOUS;
+    Cartpole env = {
+        .continuous = CONTINUOUS,
+        .cart_mass = 1.0f,
+        .pole_mass = 0.1f,
+        .pole_length = 0.5f,
+        .gravity = 9.8f,
+        .force_mag = 10.0f,
+        .tau = 0.02f,
+    };
     allocate(&env);
     c_reset(&env);
     c_render(&env);