Add sum method to running stats (#2728)

dlib/statistics/statistics.h

@@ -35,7 +35,7 @@ namespace dlib
 
         void clear()
         {
-            sum = 0;
+            sum_     = 0;
             sum_sqr  = 0;
             sum_cub  = 0;
             sum_four = 0;
@@ -49,7 +49,7 @@ namespace dlib
             const T& val
         )
         {
-            sum      += val;
+            sum_     += val;
             sum_sqr  += val*val;
             sum_cub  += cubed(val);
             sum_four += quaded(val);
@@ -68,11 +68,17 @@ namespace dlib
             return n;
         }
 
+        T sum (
+        ) const
+        {
+            return sum_;
+        }
+
         T mean (
         ) const
         {
             if (n != 0)
-                return sum/n;
+                return sum_/n;
             else
                 return 0;
         }
@@ -114,7 +120,7 @@ namespace dlib
                 );
 
             T temp = 1/(n-1);
-            temp = temp*(sum_sqr - sum*sum/n);
+            temp = temp*(sum_sqr - sum_*sum_/n);
             // make sure the variance is never negative.  This might
             // happen due to numerical errors.
             if (temp >= 0)
@@ -148,8 +154,8 @@ namespace dlib
 
             T temp  = 1/n;
             T temp1 = std::sqrt(n*(n-1))/(n-2); 
-            temp    = temp1*temp*(sum_cub - 3*sum_sqr*sum*temp + 2*cubed(sum)*temp*temp)/
-                      (std::sqrt(std::pow(temp*(sum_sqr-sum*sum*temp),3)));
+            temp    = temp1*temp*(sum_cub - 3*sum_sqr*sum_*temp + 2*cubed(sum_)*temp*temp)/
+                      (std::sqrt(std::pow(temp*(sum_sqr-sum_*sum_*temp),3)));
 
             return temp; 
         }
@@ -165,9 +171,9 @@ namespace dlib
             );
 
             T temp = 1/n;
-            T m4   = temp*(sum_four - 4*sum_cub*sum*temp+6*sum_sqr*sum*sum*temp*temp
-                     -3*quaded(sum)*cubed(temp));
-            T m2   = temp*(sum_sqr-sum*sum*temp);
+            T m4   = temp*(sum_four - 4*sum_cub*sum_*temp+6*sum_sqr*sum_*sum_*temp*temp
+                     -3*quaded(sum_)*cubed(temp));
+            T m2   = temp*(sum_sqr-sum_*sum_*temp);
             temp   = (n-1)*((n+1)*m4/(m2*m2)-3*(n-1))/((n-2)*(n-3));
 
             return temp; 
@@ -192,7 +198,7 @@ namespace dlib
         {
             running_stats temp(*this);
 
-            temp.sum += rhs.sum;
+            temp.sum_ += rhs.sum_;
             temp.sum_sqr += rhs.sum_sqr;
             temp.sum_cub += rhs.sum_cub;
             temp.sum_four += rhs.sum_four;
@@ -215,7 +221,7 @@ namespace dlib
         ); 
 
     private:
-        T sum;
+        T sum_;
         T sum_sqr;
         T sum_cub;
         T sum_four;
@@ -236,7 +242,7 @@ namespace dlib
         int version = 2;
         serialize(version, out);
 
-        serialize(item.sum, out);
+        serialize(item.sum_, out);
         serialize(item.sum_sqr, out);
         serialize(item.sum_cub, out);
         serialize(item.sum_four, out);
@@ -256,7 +262,7 @@ namespace dlib
         if (version != 2)
             throw dlib::serialization_error("Unexpected version number found while deserializing dlib::running_stats object.");
 
-        deserialize(item.sum, in);
+        deserialize(item.sum_, in);
         deserialize(item.sum_sqr, in);
         deserialize(item.sum_cub, in);
         deserialize(item.sum_four, in);

dlib/statistics/statistics_abstract.h

@@ -222,8 +222,9 @@ namespace dlib
         );
         /*!
             ensures
-                - updates the mean, variance, skewness, and kurtosis stored in this object
-                  so that the new value is factored into them.
+                - updates the sum, mean, variance, skewness, and kurtosis stored in this
+                  object so that the new value is factored into them.
+                - #sum() == sum() + val
                 - #mean() == mean()*current_n()/(current_n()+1) + val/(current_n()+1).
                   (i.e. the updated mean value that takes the new value into account)
                 - #variance() == the updated variance that takes this new value into account.
@@ -232,6 +233,14 @@ namespace dlib
                 - #current_n() == current_n() + 1
         !*/
 
+        T sum (
+        ) const;
+        /*!
+            ensures
+                - returns the sum of all the values presented to this object
+                  so far.
+        !*/
+
         T mean (
         ) const;
         /*!