Update test.md

docs/user_guide/test.md

@@ -14,4 +14,5 @@ $$
 
 Now we cite Eqn (1), and here is an inline equation: $a = \cos(\omega t)$. Let's see how it shows
 
-For each ensemble $i$, select$N_{i}$) configurations
+
+where $n=1,2,3,……,N_i$ ), by {${x_{n}}$} ($n=1,2,3,……,N$), where N is: