refs #11348. Apply the fix.

The algorithm documentation for this algorithm is actually up-to-date
correctly pointing out that the file stores the variance. The fix
brings the implementation in-line.

Code/Mantid/Framework/MDAlgorithms/src/CreateMDHistoWorkspace.cpp

@@ -49,12 +49,13 @@ const std::string CreateMDHistoWorkspace::category() const {
  */
 void CreateMDHistoWorkspace::init() {
   declareProperty(new ArrayProperty<double>("SignalInput"),
-                  "A comma separated list of all the signal values required "
-                  "for the workspace");
+                  "Signal array for n-dimensional workspace");
 
   declareProperty(new ArrayProperty<double>("ErrorInput"),
-                  "A comma separated list of all the error values required for "
-                  "the workspace");
+                  "Error array for n-dimensional workspace");
+
+  declareProperty(new ArrayProperty<double>("NumberOfEvents", std::vector<double>(0)),
+                  "Number of pixels array for n-dimensional workspace. Optional, defaults to 1 per bin.");
 
   // Declare all the generic properties required.
   this->initGenericImportProps();
@@ -65,11 +66,13 @@ void CreateMDHistoWorkspace::init() {
  */
 void CreateMDHistoWorkspace::exec() {
   MDHistoWorkspace_sptr ws = this->createEmptyOutputWorkspace();
-  double *signals = ws->getSignalArray();
-  double *errors = ws->getErrorSquaredArray();
+  Mantid::signal_t *signals = ws->getSignalArray();
+  Mantid::signal_t *errors = ws->getErrorSquaredArray();
+  Mantid::signal_t *nEvents = ws->getNumEventsArray();
 
   std::vector<double> signalValues = getProperty("SignalInput");
   std::vector<double> errorValues = getProperty("ErrorInput");
+  std::vector<double> numberOfEvents = getProperty("NumberOfEvents");
 
   size_t binProduct = this->getBinProduct();
   std::stringstream stream;
@@ -82,6 +85,15 @@ void CreateMDHistoWorkspace::exec() {
     throw std::invalid_argument("Expected size of the ErrorInput is: " +
                                 stream.str());
   }
+  if (!numberOfEvents.empty() && binProduct != numberOfEvents.size()) {
+    throw std::invalid_argument("Expected size of the NumberOfEvents is: " +
+                                stream.str() + ". Leave empty to auto fill with 1.0");
+  }
+
+  // Auto fill number of events.
+  if(numberOfEvents.empty()) {
+    numberOfEvents = std::vector<double>(binProduct, 1.0);
+  }
 
   // Copy from property
   std::copy(signalValues.begin(), signalValues.end(), signals);
@@ -93,6 +105,10 @@ void CreateMDHistoWorkspace::exec() {
   std::copy(errorValues.begin(), errorValues.end(), errors);
   // Clean up
   errorValues.swap(empty);
+  // Copy from property
+  std::copy(numberOfEvents.begin(), numberOfEvents.end(), nEvents);
+  // Clean up
+  numberOfEvents.swap(empty);
 
   setProperty("OutputWorkspace", ws);
 }

Code/Mantid/Framework/MDAlgorithms/src/LoadSQW.cpp

@@ -276,10 +276,10 @@ void
           interpretAs<float>(Buffer, current_pix + column_size),
           interpretAs<float>(Buffer, current_pix + column_size_2),
           interpretAs<float>(Buffer, current_pix + column_size_3)};
-      float error = interpretAs<float>(Buffer, current_pix + column_size_8);
+      const float errorSQ = interpretAs<float>(Buffer, current_pix + column_size_8);
       ws->addEvent(MDEvent<4>(
           interpretAs<float>(Buffer, current_pix + column_size_7), // Signal
-          error * error,                                           // Error sq
+          errorSQ,                                           // Error sq
           static_cast<uint16_t>(interpretAs<float>(
               Buffer, current_pix + column_size_6)), // run Index
           static_cast<int32_t>(interpretAs<float>(

Code/Mantid/Framework/MDAlgorithms/test/CreateMDHistoWorkspaceTest.h

@@ -81,6 +81,16 @@ public:
     AnalysisDataService::Instance().remove(outWSName);
   }
 
+  void test_throws_if_wrong_number_of_nevents()
+  {
+    std::string outWSName = "test_ws";
+    IAlgorithm_sptr alg = make_standard_algorithm(outWSName);
+    alg->setProperty("NumberOfEvents", "1"); //Only one number of events value provided, but NumberOfBins set to 5!
+    TS_ASSERT_THROWS(alg->execute(), std::invalid_argument);
+    AnalysisDataService::Instance().remove(outWSName);
+  }
+
+
   void test_exec_1D()
   {
     // Name of the output workspace.