Added cased equation to piston tension model description

diff --git a/src/sawsim.nw b/src/sawsim.nw
index 5a62b960161714daf90a5d73122c1a6472e49d75..f6d9a0de1ed6f4896b6048b4b840991fe0b62e39 100644 (file)
--- a/src/sawsim.nw
+++ b/src/sawsim.nw
@@ -4476,6 +4476,12 @@ than a particular threshold $L$, and infinite tension for $x>L$.  The
 tension at $x=L$ is undefined, but may be any positive value.  The
 model is called the ``piston'' model because it resembles a
 frictionless piston sliding in a rigid cylinder of length $L$.
+$$
+  F = \begin{cases}
+        0 & \text{if $x<L$}, \\
+        \infty & \text{if $x>L$}.
+      \end{cases}
+$$
 
 Note that because of it's infinte stiffness at $x=L$, fully extended
 domains with this tension model will be identical to completely rigid