Update data_and_models.md

doc/data_and_models.md

@@ -4,10 +4,10 @@ Currently PowerSAS.m supports extended PSAT (Matlab) data format. Support for ot
 
 ### 2. Extension of PSAT (Matlab) format
 #### 2.1 Automatic generation control (AGC) model
-Here PowerSAS provides a simple AGC model. It is named as `Agc.con` in data files and it is a N$times$4 matrix. Each column is defined as below:
+Here PowerSAS provides a simple AGC model. It is named as `Agc.con` in data files and it is a N$\times$4 matrix. Each column is defined as below:
 Column  | Content
 -------| -------------
 1 | Bus index
 2 | Reciprocal of turbine governor gain on bus
 3 | Effective damping ratio on bus
-4 | Reciprocal of AGC control time constant 
+4 | Reciprocal of AGC control time constant