Notational fix in modeling.rst by William Rucklidge.

Change-Id: Iffa127541380fcc32da13fe4ac474692e1e3d0ec

docs/source/modeling.rst

diff --git a/docs/source/modeling.rst b/docs/source/modeling.rst
index 21cda70..0d6288a 100644
--- a/docs/source/modeling.rst
+++ b/docs/source/modeling.rst
@@ -63,8 +63,9 @@
 x_{i_k}\right]`, compute the vector
 :math:`f_i\left(x_{i_1},...,x_{i_k}\right)` and the matrices
 
- .. math:: J_{ij} = \frac{\partial}{\partial x_{i_j}}f_i\left(x_{i_1},...,x_{i_k}\right),\quad \forall j \in \{i_1,..., i_k\}
-
+ .. math:: J_{ij} = \frac{\partial}{\partial
+	   x_{i_j}}f_i\left(x_{i_1},...,x_{i_k}\right),\quad \forall j
+	   \in \{1, \ldots, k\}
 
 .. class:: CostFunction