ceph/src/boost/libs/hana/example/cppcon_2014/matrix/det.hpp

   1 // Copyright Louis Dionne 2013-2016
   2 // Distributed under the Boost Software License, Version 1.0.
   3 // (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
   4
   5 #ifndef BOOST_HANA_EXAMPLE_CPPCON_2014_MATRIX_DET_HPP
   6 #define BOOST_HANA_EXAMPLE_CPPCON_2014_MATRIX_DET_HPP
   7
   8 #include <boost/hana/equal.hpp>
   9 #include <boost/hana/eval_if.hpp>
  10 #include <boost/hana/front.hpp>
  11 #include <boost/hana/functional/always.hpp>
  12 #include <boost/hana/functional/fix.hpp>
  13 #include <boost/hana/functional/flip.hpp>
  14 #include <boost/hana/functional/on.hpp>
  15 #include <boost/hana/functional/partial.hpp>
  16 #include <boost/hana/integral_constant.hpp>
  17 #include <boost/hana/plus.hpp>
  18 #include <boost/hana/power.hpp>
  19 #include <boost/hana/range.hpp>
  20 #include <boost/hana/remove_at.hpp>
  21 #include <boost/hana/transform.hpp>
  22 #include <boost/hana/tuple.hpp>
  23 #include <boost/hana/unpack.hpp>
  24
  25 #include <utility>
  26
  27 #include "matrix.hpp"
  28
  29
  30 namespace cppcon {
  31     namespace hana = boost::hana;
  32     auto det = hana::fix([](auto det, auto&& m) -> decltype(auto) {
  33         auto matrix_minor = [=](auto&& m, auto i, auto j) -> decltype(auto) {
  34             return det(hana::unpack(
  35                 hana::transform(
  36                     hana::remove_at(rows(std::forward<decltype(m)>(m)), i),
  37                     hana::partial(hana::flip(hana::remove_at), j)
  38                 ),
  39                 matrix
  40             ));
  41         };
  42
  43         auto cofactor = [=](auto&& m, auto i, auto j) {
  44             return hana::power(hana::int_c<-1>, hana::plus(i, j)) *
  45                     matrix_minor(std::forward<decltype(m)>(m), i, j);
  46         };
  47
  48         return hana::eval_if(m.size() == hana::size_c<1>,
  49             hana::always(m.at(hana::size_c<0>, hana::size_c<0>)),
  50             [=](auto _) {
  51                 auto cofactors_1st_row = hana::unpack(_(hana::make_range)(hana::size_c<0>, m.ncolumns()),
  52                     hana::on(hana::make_tuple, hana::partial(cofactor, m, hana::size_c<0>))
  53                 );
  54                 return detail::tuple_scalar_product(hana::front(rows(m)), cofactors_1st_row);
  55             }
  56         );
  57     });
  58 } // end namespace cppcon
  59
  60 #endif // !BOOST_HANA_EXAMPLE_CPPCON_2014_MATRIX_DET_HPP