Improve documentation and diagram

Refs #22197

Framework/Algorithms/src/Stitch1D.cpp

 #include "MantidAlgorithms/Stitch1D.h"
 #include "MantidAPI/AnalysisDataService.h"
 #include "MantidAPI/MatrixWorkspace.h"
-#include "MantidAPI/Workspace.h"
-#include "MantidAPI/WorkspaceFactory.h"
 #include "MantidAPI/WorkspaceProperty.h"
 #include "MantidHistogramData/HistogramE.h"
 #include "MantidHistogramData/HistogramDx.h"
@@ -58,7 +56,7 @@ DECLARE_ALGORITHM(Stitch1D)
  */
 MatrixWorkspace_sptr Stitch1D::maskAllBut(int a1, int a2,
                                           MatrixWorkspace_sptr &source) {
-  MatrixWorkspace_sptr product = WorkspaceFactory::Instance().create(source);
+  MatrixWorkspace_sptr product = source->clone();
   const int histogramCount = static_cast<int>(source->getNumberHistograms());
   PARALLEL_FOR_IF(Kernel::threadSafe(*source, *product))
   for (int i = 0; i < histogramCount; ++i) {
@@ -637,7 +635,6 @@ void Stitch1D::exec() {
         findStartEndIndexes(startOverlap, endOverlap, lhs);
     int a1 = boost::tuples::get<0>(startEnd);
     int a2 = boost::tuples::get<1>(startEnd);
-
     // Mask out everything BUT the overlap region as a new workspace.
     MatrixWorkspace_sptr overlap1 = maskAllBut(a1, a2, lhs);
     // Mask out everything BUT the overlap region as a new workspace.

docs/source/algorithms/Stitch1D-v3.rst

@@ -20,7 +20,7 @@ are taken to be the region of X-axis intersection.
 
 The type of the input workspaces (histogram or point data) determines the x values in the overlap range of the output workspace.
 
-The algorithm workflow is as follows:
+The algorithm workflow for histograms is as follows:
 
 #. The workspaces are initially rebinned, as prescribed by the rebin :literal:`Params`. Note that
    rebin parameters are determined automatically if not provided. In this case, the step size is
@@ -44,14 +44,13 @@ The algorithm workflow is as follows:
 #. The weighted mean of the two workspaces in range [:literal:`StartOverlap`, :literal:`EndOverlap`]
    is calculated. Note that if both workspaces have zero errors, an un-weighted mean will be
    performed instead.
-#. For histograms, the output workspace will be created by summing the left-hand-side workspace (values in range
+#. The output workspace will be created by summing the left-hand-side workspace (values in range
    [:literal:`StartX`, :literal:`StartOverlap`], where :literal:`StartX` is the minimum X value
    specified via :literal:`Params` or calculated from the left-hand-side workspace) + weighted
    mean workspace + right-hand-side workspace (values in range [:literal:`EndOverlap`, :literal:`EndX`],
    where :literal:`EndX` is the maximum X value specified via :literal:`Params` or calculated
    from the right-hand-side workspace) multiplied by the scale factor.
    Dx values will not be present in the output workspace.
-   For point data, the output workspace will propagate x values and Dx values present in the overlap range to the output workspace.
 #. The special values are put back in the output workspace. Note that if both the left-hand-side
    workspace and the right-hand-side workspace happen to have a different special value in the same bin, this
    bin will be set to infinite in the output workspace.
@@ -63,6 +62,22 @@ workflow with a manual scale factor specified by the user.
 
 .. diagram:: Stitch1D-v3.dot
 
+The algorithm workflow for point data is as follows:
+
+#. If :literal:`UseManualScaleFactor` was set to false, both workspaces will be integrated
+   according to the integration range defined by :literal:`StartOverlap` and :literal:`EndOverlap`.
+   Note that the integration is performed without special values, as those have been masked out
+   in the previous step. The scale factor is then calculated as the quotient of the integral of
+   the left-hand-side workspace by the integral of the right-hand-side workspace (or the quotient
+   of the right-hand-side workspace by the left-hand-side workspace if :literal:`ScaleRHSWorkspace`
+   was set to false), and the right-hand-side workspace (left-hand-side if :literal:`ScaleRHSWorkspace`
+   was set to false) is multiplied by the calculated factor.
+#. Alternatively, if :literal:`UseManualScaleFactor` was set to true, the scale factor is applied
+   to the right-hand-side workspace (left-hand-side workspace if :literal:`ScaleRHSWorkspace` was
+   set to false).
+#. The output workspace will be created by joining and sorted to guarantee ascending x values.
+   Dx values will be present in the output workspace.
+
 Error propagation
 #################
 
@@ -94,7 +109,7 @@ Usage
    ws1 = CreateWorkspace(UnitX="1/q", DataX=x1, DataY=gaussian(x1[:-1], 0, 0.1)+1)
    ws2 = CreateWorkspace(UnitX="1/q", DataX=x2, DataY=gaussian(x2[:-1], 1, 0.05)+1)
 
-   #stitch the histograms together
+   # stitch the histograms together
    stitched, scale = Stitch1D(LHSWorkspace=ws1, RHSWorkspace=ws2, StartOverlap=0.4, EndOverlap=0.6, Params=0.02)
 
    # plot the individual workspaces alongside the stitched one
@@ -128,7 +143,7 @@ Usage
    ws1 = CreateWorkspace(UnitX="1/q", DataX=x1, DataY=gaussian(x1, 0, 0.1)+1)
    ws2 = CreateWorkspace(UnitX="1/q", DataX=x2, DataY=gaussian(x2, 1, 0.05)+1)
 
-   #stitch the histograms together
+   # stitch the histograms together
    stitched, scale = Stitch1D(LHSWorkspace=ws1, RHSWorkspace=ws2, StartOverlap=0.4, EndOverlap=0.6)
 
    # plot the individual workspaces alongside the stitched one
@@ -137,7 +152,7 @@ Usage
    axs[0].plot(mtd['ws1'], wkspIndex=0, label='ws1')
    axs[0].plot(mtd['ws2'], wkspIndex=0, label='ws2')
    axs[0].legend()
-   axs[1].plot(mtd['stitched'], wkspIndex=0, color='k', label='stitched')
+   axs[1].plot(mtd['stitchedP'], wkspIndex=0, color='k', marker='.', ls='', label='stitched')
    axs[1].legend()
 
    # uncomment the following line to show the plot window

docs/source/diagrams/Stitch1D-v3.dot

 digraph Stitch1D {
 splines=false
-label = "\nStitch1D workflow - no manual scale factor                                                                                                                  Stitch1D workflow - manual scale factor given\n\n"
+label = "\nStitch1D workflow for histograms - no manual scale factor                                                                                                                  Stitch1D workflow histograms - manual scale factor given\n\n"
  $global_style
 
 subgraph params {