[Boost-commit] svn:boost r82781 - sandbox/variadic_templates/sandbox/array_dyn

Subject: [Boost-commit] svn:boost r82781 - sandbox/variadic_templates/sandbox/array_dyn
From: cppljevans_at_[hidden]
Date: 2013-02-07 19:39:15

Author: cppljevans
Date: 2013-02-07 19:39:15 EST (Thu, 07 Feb 2013)
New Revision: 82781
URL: http://svn.boost.org/trac/boost/changeset/82781

Log:
Used by reduce_axis.cpp (possible arg to reduce_test).

Added:
   sandbox/variadic_templates/sandbox/array_dyn/reducer_variance.hpp   (contents, props changed)

Added: sandbox/variadic_templates/sandbox/array_dyn/reducer_variance.hpp
==============================================================================
--- (empty file)
+++ sandbox/variadic_templates/sandbox/array_dyn/reducer_variance.hpp	2013-02-07 19:39:15 EST (Thu, 07 Feb 2013)
@@ -0,0 +1,134 @@
+//reducer_variance::operator(iter b,iter e) calculates variance of *b...*(e-1)
+#ifndef REDUCER_VARIANCE_HPP_INCLUDED
+#define REDUCER_VARIANCE_HPP_INCLUDED
+#include <algorithm>//for_each
+
+  template
+  < typename Value
+  >
+struct reduce_add_one
+/**@brief
+ *  add values.
+ */
+{
+      Value& 
+    my_value
+      ;
+    reduce_add_one
+    ( Value&a_value
+    )
+    : my_value
+      ( a_value
+      )
+    {}
+      Value 
+    operator()(Value operand)
+    {
+        my_value+=operand;
+        return my_value;
+    }
+};
+  template
+  < typename Value
+  >
+struct reduce_var_one
+/**@brief
+ *  sum square of deviation from a mean.
+ */
+{
+      Value&
+    my_value
+      //result value
+      ;
+      Value const
+    my_mean
+      //the mean
+      ;
+    reduce_var_one
+    ( Value&a_value//sum of square of devitation from mean
+    , Value a_mean=0
+    )
+    : my_value
+      ( a_value
+      )
+    , my_mean
+      ( a_mean
+      )
+    {}
+      Value 
+    operator()(Value operand)
+    {
+          Value 
+        deviation=operand-my_mean;
+        my_value+=deviation*deviation;
+        return my_value;
+    }
+};
+struct reducer_variance
+{
+      unsigned const
+    my_bessel_correction
+      /**@brief
+       *  == 0 or 1, indicating whether to use
+       *  Bessel's correction:
+       *    http://en.wikipedia.org/wiki/Bessel%27s_correction
+       *  if == 0, don't correct.
+       *  if == 1, then do correct.
+       */
+      ;
+    reducer_variance
+      ( bool a_bessel_correction=false
+      )
+      : my_bessel_correction(a_bessel_correction?1:0)
+      {}
+      template
+      < typename Iter
+      >
+      typename Iter::value_type
+    operator()
+      ( Iter beg
+      , Iter end
+      )const
+      /**@brief
+       *  return value == variance of data in sample, *beg ... *(end-1).
+       */
+      {
+            auto
+          sample_size=beg.distance(end);
+          assert(sample_size > my_bessel_correction);
+              typedef
+            typename Iter::value_type
+          val_t
+            ;
+            val_t
+          mean_v=0
+            ;
+            reduce_add_one<val_t>
+          reduce_add_v(mean_v)
+            ;
+          std::for_each
+            ( beg
+            , end
+            , reduce_add_v
+            );
+          mean_v=mean_v/sample_size
+            //mean_v = mean of data in *beg ... *(end-1)
+            ;
+            val_t
+          var_v;
+            reduce_var_one<val_t>
+          reduce_var_v(var_v,mean_v)
+            ;
+          std::for_each
+            ( beg
+            , end
+            , reduce_var_v
+            );
+          var_v=var_v/(sample_size-my_bessel_correction)
+            //var_v = variance of data in *beg ... *(end-1)
+            ;
+          return var_v;
+      }
+};
+        
+#endif