Improved doc. Refs #10028.

Code/Mantid/docs/source/algorithms/GenerateEventsFilter-v1.rst

@@ -81,8 +81,24 @@ this algorithm:
    equal or within the tolerance of the log value as v\_0 + n x delta\_v
    +/- tolerance\_v.
 
+
+Generate event filters by sample log value
+==========================================
+
+The sample log will be divided to intervals as :math:`v_0, v_1, \cdots, v_{i-1}, v_i, v_{i+1}, \cdots`. 
+All log entries, whose values falls into range :math:`[v_j, v_{j+1})`, will be assigned to
+a same workspace group. 
+
+
+
+Parameters and Examples
+#######################
+
+Here are the introductions to some important parameters (i.e., algorithm's properties). 
+
+
 Parameter: *Centre*
-###################
+===================
 
 The input Boolean parameter *centre* is for filtering by log value(s).
 If option *centre* is taken, then for each interval,
@@ -93,18 +109,39 @@ If option *centre* is taken, then for each interval,
 It is a shift to left.
 
 Parameter: *LogValueTolerance* and *LogValueInterval*
-#####################################################
+=====================================================
 
 These two parameters are used to determine the log value intervals for
 filtering events.
 
-Let user-specified minimum log value to be 'min', LogValueTolerance to
-be 'tol', and LogValueInterval to be 'delta', then the log value
-intervals are (min-tol, min-tol+delta), (min-tol+delta, min-tol+2delta),
-...
+Let user-specified minimum log value to be :math:`L_{min}`, 
+LogValueTolerance to be :math:`t`, and LogValueInterval to be :math:`\delta`, 
+then the log value intervals are 
+
+.. math:: [L_{min}-t, L_{min}-tol+\delta), [L_{min}-tol+\delta, L_{min}-tol+2\cdot\delta), \cdots
 
 The default value of LogValueTolerance is LogValueInterval divided by 2.
 
+Example: Filter by log value from :math:`s_0` to :math:`s_f`
+===========================================================
+
+There are two setup to acquire the same result: 
+
+- Use single-log-value mode:
+
+  - MinimumLogValue = :math:`s_0`
+  - MaximumLogValue = :math:`s_f`
+  - LogValueInterval is left to default
+
+- Use multiple-log-value mode:
+
+  - MinimumLogValue = :math:`s_0`
+  - MaximumLogValue = :math:`s_f`
+  - LogValueInterval = :math:`s_f - s_0`
+  - LogValueTolerance = 0
+
+
+
 About how log value is recorded
 ###############################