Added operator+= to discriminant_pca.

dlib/statistics/dpca.h

@@ -346,7 +346,7 @@ namespace dlib
             serialize( item.within_weight, out);
         }
 
-        const discriminant_pca operator+ (
+        discriminant_pca operator+ (
             const discriminant_pca& item
         ) const
         {
@@ -408,6 +408,14 @@ namespace dlib
             return temp;
         }
 
+        discriminant_pca& operator+= (
+            const discriminant_pca& rhs
+        )
+        {
+            (*this + rhs).swap(*this);
+            return *this;
+        }
+
     private:
 
         void compute_dpca_matrix (

dlib/statistics/dpca_abstract.h

@@ -281,7 +281,7 @@ namespace dlib
                   reduction to num_rows dimensions.
         !*/
 
-        const discriminant_pca operator+ (
+        discriminant_pca operator+ (
             const discriminant_pca& item
         ) const;
         /*!
@@ -298,6 +298,20 @@ namespace dlib
                   been done to R.
         !*/
 
+        discriminant_pca& operator+= (
+            const discriminant_pca& rhs
+        );
+        /*!
+            requires
+                - in_vector_size() == 0 || rhs.in_vector_size() == 0 || in_vector_size() == rhs.in_vector_size()
+                  (i.e. the in_vector_size() of *this and rhs must match or one must be zero)
+                - between_class_weight() == rhs.between_class_weight()
+                - within_class_weight() == rhs.within_class_weight()
+            ensures
+                - #*this == *item + rhs
+                - returns #*this
+        !*/
+
         void swap (
             discriminant_pca& item
         );

dlib/test/discriminant_pca.cpp

@@ -252,7 +252,7 @@ namespace
 
             matrix<double> mat, mat2;
 
-            sum_dpca = dpca_type() + dpca_type() + add_dpca1 + dpca_type() + add_dpca2 + add_dpca3 + add_dpca4;
+            sum_dpca += dpca_type() + dpca_type() + add_dpca1 + dpca_type() + add_dpca2 + add_dpca3 + add_dpca4;
             dpca.set_within_class_weight(0);
             dpca.set_between_class_weight(0);
             sum_dpca.set_within_class_weight(0);