documentation updated according to changes

refs #15767

MantidQt/CustomInterfaces/src/EnggDiffraction/EnggDiffractionViewQtGUI.cpp

@@ -1320,7 +1320,7 @@ void MantidQt::CustomInterfaces::EnggDiffractionViewQtGUI::
       bankDir = (bankDir).expand(selectedfPath.parent().toString());
 #endif
 
-      if (!splitBaseName.empty()) {
+      if (!splitBaseName.empty() && splitBaseName.size() > 3) {
         std::string foc_file = splitBaseName[0] + "_" + splitBaseName[1] + "_" +
                                splitBaseName[2] + "_" + splitBaseName[3];
         updateFittingDirVec(bankDir.toString(), foc_file);
@@ -1330,8 +1330,7 @@ void MantidQt::CustomInterfaces::EnggDiffractionViewQtGUI::
       // if given a run number instead
       updateFittingDirVec(m_focusDir, focusedFile.toStdString());
     } else {
-
-      userWarning("Invalid directory or run number: ",
+      userWarning("Invalid Input",
                   "Invalid directory or run number given. "
                   "Please try again");
     }

docs/source/interfaces/Engineering_Diffraction.rst

@@ -273,10 +273,11 @@ providing a list of dSpacing values where Bragg peaks are expected.
 The algorithm :ref:`EnggFitPeaks<algm-EnggFitPeaks>` used in the
 background fit peaks in those areas using a peak fitting function.
 
-To use the Fitting tab, user is required to provide a focused workspace
-as Focus Run input, list of expected peaks which can be either by browsing
-a (*CSV*) file or entering within the text-field and simply click on the Fit
-button.
+To use the Fitting tab, user is required to provide:
+
+1. A focused file as Focus Run input by browsing or entering run number
+2. List of expected peaks which can be either by browsing a (*CSV*) file
+   or entering within the text-field simply click on the Fit button.
 
 Parameters
 ^^^^^^^^^^
@@ -285,16 +286,26 @@ These parameters are required to process Fitting successfully:
 
 Focused Run #:
   Focused workspace directory or selected with the help of browse button.
+  User may also select the file by simply entering the file run number.
   Focused workspace can be generated with the help of
   :ref:`focus-Engineering_Diffraction-ref` tab, the output folder
   directory can be set in the :ref:`setting-Engineering_Diffraction-ref`
   tab under the *Focusing settings* section.
+  The interface will automatically select all the bank files found with the
+  same run-number and update the Plot Bank combo-box and Bank list
+  accordingly.
 
 Peaks:
   A list of dSpacing values to be translated into TOF to find expected
   peaks. These peaks can be manually written or imported by selecting a
   (*CSV*) file.
 
+Plot Bank/Bank List:
+  These GUI widgets will only be enabled when multiple focused bank
+  files are found within the working directory or focused output directory.
+  This would enable user to select the desired bank which they would like to
+  plot with the help of Plot Bank combo-box or Bank List.
+
 Output
 ^^^^^^