From 64c33cefcfb6edfcaf424927615621d94ad39d21 Mon Sep 17 00:00:00 2001
From: Yuval Tassa <tassa@google.com>
Date: Tue, 12 Dec 2023 03:55:19 -0800
Subject: [PATCH] Correct formula for `solref` direct stiffness. Fixes #732.

PiperOrigin-RevId: 590144795
Change-Id: I94def777c7456243509374caecea2a335859f1f2
---
 doc/modeling.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/doc/modeling.rst b/doc/modeling.rst
index c43b9a04..681534cd 100644
--- a/doc/modeling.rst
+++ b/doc/modeling.rst
@@ -403,7 +403,7 @@ and the damping ratio is ignored. Equivalently, in the direct format, the :math:
    .. math::
       \begin{aligned}
       b &= \text{damping} / d_\text{width} \\
-      k &= \text{stiffness} / d_\text{width}^2 \\
+      k &= \text{stiffness} \cdot d(r) / d_\text{width}^2 \\
       \end{aligned}
 
 .. tip::