Update 4.6MBAR.md

docs/user_guide/4.6MBAR.md

@@ -20,7 +20,7 @@ c_i = \int dx \cdot w_i(x) \\
 p_i(x) = \frac{w_i(x)}{c_i} 
 $$
 
-For each ensemble $i$, select $N_{i}$ configurations, represented by ${x_{in}}$ (where $n=1,2,3,……,N_i$ ), and the total number of configurations across ensembles is represented by {${x_{n}}$} ($n=1,2,3,……,N$), where N is:
+For each ensemble $i$, select $N_{i}$ configurations, represented by ${x_{in}}$ (where $n=1,2,3,…,N_i$ ), and the total number of configurations across ensembles is represented by {${x_{n}}$} ($n=1,2,3,……,N$), where N is:
 
 $$
 N = \sum_{i=1}^{K} N_i \label{eq-3}