comparison DEPENDENCIES/generic/include/boost/accumulators/statistics/skewness.hpp @ 16:2665513ce2d3

Add boost headers

+///////////////////////////////////////////////////////////////////////////////
+// skewness.hpp
+//
+//  Copyright 2006 Olivier Gygi, Daniel Egloff. Distributed under the Boost
+//  Software License, Version 1.0. (See accompanying file
+//  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_ACCUMULATORS_STATISTICS_SKEWNESS_HPP_EAN_28_10_2005
+#define BOOST_ACCUMULATORS_STATISTICS_SKEWNESS_HPP_EAN_28_10_2005
+
+#include <limits>
+#include <boost/mpl/placeholders.hpp>
+#include <boost/accumulators/framework/accumulator_base.hpp>
+#include <boost/accumulators/framework/extractor.hpp>
+#include <boost/accumulators/framework/parameters/sample.hpp>
+#include <boost/accumulators/numeric/functional.hpp>
+#include <boost/accumulators/framework/depends_on.hpp>
+#include <boost/accumulators/statistics_fwd.hpp>
+#include <boost/accumulators/statistics/moment.hpp>
+#include <boost/accumulators/statistics/mean.hpp>
+
+
+namespace boost { namespace accumulators
+{
+
+namespace impl
+{
+    ///////////////////////////////////////////////////////////////////////////////
+    // skewness_impl
+    /**
+        @brief Skewness estimation
+
+        The skewness of a sample distribution is defined as the ratio of the 3rd central moment and the \f$ 3/2 \f$-th power
+        of the 2nd central moment (the variance) of the samples 3. The skewness can also be expressed by the simple moments:
+
+        \f[
+            \hat{g}_1 =
+                \frac
+                {\widehat{m}_n^{(3)}-3\widehat{m}_n^{(2)}\hat{\mu}_n+2\hat{\mu}_n^3}
+                {\left(\widehat{m}_n^{(2)} - \hat{\mu}_n^{2}\right)^{3/2}}
+        \f]
+
+        where \f$ \widehat{m}_n^{(i)} \f$ are the \f$ i \f$-th moment and \f$ \hat{\mu}_n \f$ the mean (first moment) of the
+        \f$ n \f$ samples.
+    */
+    template<typename Sample>
+    struct skewness_impl
+      : accumulator_base
+    {
+        // for boost::result_of
+        typedef typename numeric::functional::fdiv<Sample, Sample>::result_type result_type;
+
+        skewness_impl(dont_care)
+        {
+        }
+
+        template<typename Args>
+        result_type result(Args const &args) const
+        {
+            return numeric::fdiv(
+                        accumulators::moment<3>(args)
+                        - 3. * accumulators::moment<2>(args) * mean(args)
+                        + 2. * mean(args) * mean(args) * mean(args)
+                      , ( accumulators::moment<2>(args) - mean(args) * mean(args) )
+                        * std::sqrt( accumulators::moment<2>(args) - mean(args) * mean(args) )
+                   );
+        }
+    };
+
+} // namespace impl
+
+///////////////////////////////////////////////////////////////////////////////
+// tag::skewness
+//
+namespace tag
+{
+    struct skewness
+      : depends_on<mean, moment<2>, moment<3> >
+    {
+        /// INTERNAL ONLY
+        ///
+        typedef accumulators::impl::skewness_impl<mpl::_1> impl;
+    };
+}
+
+///////////////////////////////////////////////////////////////////////////////
+// extract::skewness
+//
+namespace extract
+{
+    extractor<tag::skewness> const skewness = {};
+
+    BOOST_ACCUMULATORS_IGNORE_GLOBAL(skewness)
+}
+
+using extract::skewness;
+
+// So that skewness can be automatically substituted with
+// weighted_skewness when the weight parameter is non-void
+template<>
+struct as_weighted_feature<tag::skewness>
+{
+    typedef tag::weighted_skewness type;
+};
+
+template<>
+struct feature_of<tag::weighted_skewness>
+  : feature_of<tag::skewness>
+{
+};
+
+}} // namespace boost::accumulators
+
+#endif