corrected typo in NN slides

doc/pub/NeuralNet/html/NeuralNet.html

@@ -266,7 +266,7 @@ MathJax.Hub.Config({
 <center>[2] <b>Department of Physics and Astronomy and National Superconducting Cyclotron Laboratory, Michigan State University</b></center>
 <br>
 <p>
-<center><h4>Sep 18, 2019</h4></center> <!-- date -->
+<center><h4>Sep 27, 2019</h4></center> <!-- date -->
 <br>
 <p>
 <!-- !split --><br><br><br><br><br><br><br><br><br><br>
@@ -1148,7 +1148,7 @@ $$
 
 and recalling that
 $$
-z_j^{l+1} = \sum_{i=1}^{M_{l}}w_{ij}^{l+1}a_j^{l}+b_j^{l+1},
+z_j^{l+1} = \sum_{i=1}^{M_{l}}w_{ij}^{l+1}a_i^{l}+b_j^{l+1},
 $$
 
 with \( M_l \) being the number of nodes in layer \( l \), we obtain