Re: 5285 Add convertToBinBoundary() to VectorHelper

Since VectorHelper::rebin() requires current X vector with
one more entry than the current Y vector, even if the
Workspace2D is a distribution, we need to adjust the current
X vector before calling rebin.  This is a convenience method
that essentially reverses the convertToBinCentre() method, so
it seems to belong in VectorHelper.
refs #5285

Code/Mantid/Framework/DataObjects/src/Workspace2D.cpp

@@ -146,9 +146,21 @@ namespace Mantid
       if (X.size() <= 1) throw std::runtime_error("Workspace2D::generateHistogram(): X vector must be at least length 2");
       Y.resize(X.size()-1, 0);
       E.resize(X.size()-1, 0);
-      // Perform the rebin from the current bins to the new ones
-      Mantid::Kernel::VectorHelper::rebin(currentX,currentY,currentE, X, Y, E,
-          this->isDistribution());
+
+                                                  // Perform the rebin from the current bins to the new ones
+      if ( currentX.size() == currentY.size() )   // First, convert to bin boundaries if needed.  The 
+      {                                           // VectorHelper::rebin, assumes bin boundaries, even if 
+        std::vector<double> histX;                // it is a distribution!
+        histX.resize( currentX.size() + 1 );
+        Mantid::Kernel::VectorHelper::convertToBinBoundary( currentX, histX );
+        Mantid::Kernel::VectorHelper::rebin( histX, currentY, currentE, X, Y, E, 
+                                             this->isDistribution() );
+      }
+      else                                        // assume x_size = y_size + 1
+      {
+        Mantid::Kernel::VectorHelper::rebin( currentX, currentY, currentE, X, Y, E, 
+                                             this->isDistribution() );
+      }
     }
 
 

Code/Mantid/Framework/Kernel/inc/MantidKernel/VectorHelper.h

@@ -55,6 +55,10 @@ namespace VectorHelper
 
   /// Convert an array of bin boundaries to bin centre values.
   void MANTID_KERNEL_DLL convertToBinCentre(const std::vector<double> & bin_edges, std::vector<double> & bin_centres);
+
+  /// Convert an array of bin centers to bin boundary values.
+  void MANTID_KERNEL_DLL convertToBinBoundary(const std::vector<double> & bin_centers, std::vector<double> & bin_edges);
+
   bool MANTID_KERNEL_DLL isConstantValue(const MantidVec &arra);
 
   template <typename NumT>

Code/Mantid/Framework/Kernel/src/VectorHelper.cpp

@@ -332,6 +332,41 @@ void convertToBinCentre(const std::vector<double> & bin_edges, std::vector<doubl
   bin_centres.erase(bin_centres.begin());
 }
 
+
+//-------------------------------------------------------------------------------------------------
+/**
+ * Convert the given set of bin centers into bin boundary values.
+ * NOTE: the first and last bin boundaries are calculated so 
+ * that the first and last bin centers are in the center of the
+ * first and last bins, respectively. For a particular set of
+ * bin centers, this may not be correct, but it is the best that
+ * can be done, lacking any other information.
+ *
+ * @param bin_centres :: A vector of values specifying bin centers.
+ * @param bin_edges   :: An output vector of values specifying bin 
+ *                       boundaries
+ *
+ */
+void convertToBinBoundary(const std::vector<double> & bin_centers, std::vector<double> & bin_edges)
+{
+  const std::vector<double>::size_type n = bin_centers.size();
+  if( bin_edges.size() != ( n + 1 ) )
+  {
+    bin_edges.resize( n + 1 );
+  }
+
+  for( size_t i = 0; i < n - 1; ++i )
+  {
+    bin_edges[i+1] = 0.5*(bin_centers[i] + bin_centers[i+1]);
+  }
+
+  bin_edges[0] = bin_centers[0] - (bin_edges[1] - bin_centers[0]);
+
+  bin_edges[ n ] = bin_centers[ n - 1 ] + 
+                 ( bin_centers[ n - 1 ] - bin_edges[ n - 1 ] );
+}
+
+
 //-------------------------------------------------------------------------------------------------
 /** Assess if all the values in the vector are equal or if there are some different values
 *  @param[in] arra the vector to examine