I implemented the operator operator comparison operator< for Eigen::VectorXd , and sometimes I need to pass the comparison function to another function, I'm tired of wrapping operator< in [](const VectorXd& v1, const VectorXd& v2)->bool{return v1 < v2} , so I think std::less would be useful since, as far as I understand, it can generate a lambda function until operator< defined.
However, I found that std::less<VectorXd> does not work for me, for example, the following code works fine:
#include "Eigen/Dense" #include <iostream> #include <functional> using namespace std; using namespace Eigen; struct T { int x; }; bool operator<(const T& t1, const T& t2) { return t1.x < t2.x; } bool operator<(const VectorXd& v1, const VectorXd& v2) { return (v1.array() <= v2.array()).all() and (v1 != v2); } int main() { T t1, t2; t1.x = 3; t2.x = 2; auto ft = std::less<T>(); cout << ft(t1, t2) << endl; return EXIT_SUCCESS; }
However, if I use std::less<VectorXd> as follows:
#include "Eigen/Dense" #include <iostream> #include <functional> using namespace std; using namespace Eigen; struct T { int x; }; bool operator<(const T& t1, const T& t2) { return t1.x < t2.x; } bool operator<(const VectorXd& v1, const VectorXd& v2) { return (v1.array() <= v2.array()).all() and (v1 != v2); } int main() { T t1, t2; t1.x = 3; t2.x = 2; auto ft = std::less<T>(); cout << ft(t1, t2) << endl; VectorXd v1(3); VectorXd v2(3); v1 << 1, 2, 3; v2 << 2, 3, 4; auto fv = std::less<VectorXd>(); cout << fv(v1, v2) << endl; return EXIT_SUCCESS; }
The code fails to compile, and I get error messages as shown below:
In file included from /usr/include/c++/5/string:48:0, from /usr/include/c++/5/bits/locale_classes.h:40, from /usr/include/c++/5/bits/ios_base.h:41, from /usr/include/c++/5/ios:42, from /usr/include/c++/5/istream:38, from /usr/include/c++/5/sstream:38, from /usr/include/c++/5/complex:45, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Core:80, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Dense:1, from test.cpp:1: /usr/include/c++/5/bits/stl_function.h: In instantiation of 'bool std::less<_Tp>::operator()(const _Tp&, const _Tp&) const [with _Tp = Eigen::Matrix<double, -1, 1>]': test.cpp:36:26: required from here /usr/include/c++/5/bits/stl_function.h:387:20: error: no match for 'operator<' (operand types are 'const Eigen::Matrix<double, -1, 1>' and 'const Eigen::Matrix<double, -1, 1>') { return __x < __y; } ^ In file included from /usr/include/c++/5/bits/stl_algobase.h:64:0, from /usr/include/c++/5/bits/char_traits.h:39, from /usr/include/c++/5/ios:40, from /usr/include/c++/5/istream:38, from /usr/include/c++/5/sstream:38, from /usr/include/c++/5/complex:45, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Core:80, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Dense:1, from test.cpp:1: /usr/include/c++/5/bits/stl_pair.h:220:5: note: candidate: template<class _T1, class _T2> constexpr bool std::operator<(const std::pair<_T1, _T2>&, const std::pair<_T1, _T2>&) operator<(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y) ^ /usr/include/c++/5/bits/stl_pair.h:220:5: note: template argument deduction/substitution failed: In file included from /usr/include/c++/5/string:48:0, from /usr/include/c++/5/bits/locale_classes.h:40, from /usr/include/c++/5/bits/ios_base.h:41, from /usr/include/c++/5/ios:42, from /usr/include/c++/5/istream:38, from /usr/include/c++/5/sstream:38, from /usr/include/c++/5/complex:45, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Core:80, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Dense:1, from test.cpp:1: /usr/include/c++/5/bits/stl_function.h:387:20: note: 'const Eigen::Matrix<double, -1, 1>' is not derived from 'const std::pair<_T1, _T2>' { return __x < __y; } ^ In file included from /usr/include/c++/5/bits/stl_algobase.h:67:0, from /usr/include/c++/5/bits/char_traits.h:39, from /usr/include/c++/5/ios:40, from /usr/include/c++/5/istream:38, from /usr/include/c++/5/sstream:38, from /usr/include/c++/5/complex:45, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Core:80, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Dense:1, from test.cpp:1: /usr/include/c++/5/bits/stl_iterator.h:298:5: note: candidate: template<class _Iterator> bool std::operator<(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_Iterator>&) operator<(const reverse_iterator<_Iterator>& __x, ^ /usr/include/c++/5/bits/stl_iterator.h:298:5: note: template argument deduction/substitution failed: In file included from /usr/include/c++/5/string:48:0, from /usr/include/c++/5/bits/locale_classes.h:40, from /usr/include/c++/5/bits/ios_base.h:41, from /usr/include/c++/5/ios:42, from /usr/include/c++/5/istream:38, from /usr/include/c++/5/sstream:38, from /usr/include/c++/5/complex:45, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Core:80, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Dense:1, from test.cpp:1: /usr/include/c++/5/bits/stl_function.h:387:20: note: 'const Eigen::Matrix<double, -1, 1>' is not derived from 'const std::reverse_iterator<_Iterator>' { return __x < __y; } ^ In file included from /usr/include/c++/5/bits/stl_algobase.h:67:0, from /usr/include/c++/5/bits/char_traits.h:39, from /usr/include/c++/5/ios:40, from /usr/include/c++/5/istream:38, from /usr/include/c++/5/sstream:38, from /usr/include/c++/5/complex:45, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Core:80, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Dense:1, from test.cpp:1: /usr/include/c++/5/bits/stl_iterator.h:348:5: note: candidate: template<class _IteratorL, class _IteratorR> bool std::operator<(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_IteratorR>&) operator<(const reverse_iterator<_IteratorL>& __x, ^ /usr/include/c++/5/bits/stl_iterator.h:348:5: note: template argument deduction/substitution failed: In file included from /usr/include/c++/5/string:48:0, from /usr/include/c++/5/bits/locale_classes.h:40, from /usr/include/c++/5/bits/ios_base.h:41, from /usr/include/c++/5/ios:42, from /usr/include/c++/5/istream:38, from /usr/include/c++/5/sstream:38, from /usr/include/c++/5/complex:45, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Core:80, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Dense:1, from test.cpp:1: /usr/include/c++/5/bits/stl_function.h:387:20: note: 'const Eigen::Matrix<double, -1, 1>' is not derived from 'const std::reverse_iterator<_Iterator>' { return __x < __y; } ^ In file included from /usr/include/c++/5/bits/stl_algobase.h:67:0, from /usr/include/c++/5/bits/char_traits.h:39, from /usr/include/c++/5/ios:40, from /usr/include/c++/5/istream:38, from /usr/include/c++/5/sstream:38, from /usr/include/c++/5/complex:45, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Core:80, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Dense:1, from test.cpp:1: /usr/include/c++/5/bits/stl_iterator.h:1089:5: note: candidate: template<class _IteratorL, class _IteratorR> bool std::operator<(const std::move_iterator<_Iterator>&, const std::move_iterator<_IteratorR>&) operator<(const move_iterator<_IteratorL>& __x, ^ /usr/include/c++/5/bits/stl_iterator.h:1089:5: note: template argument deduction/substitution failed: In file included from /usr/include/c++/5/string:48:0, from /usr/include/c++/5/bits/locale_classes.h:40, from /usr/include/c++/5/bits/ios_base.h:41, from /usr/include/c++/5/ios:42, from /usr/include/c++/5/istream:38, from /usr/include/c++/5/sstream:38, from /usr/include/c++/5/complex:45, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Core:80, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Dense:1, from test.cpp:1: /usr/include/c++/5/bits/stl_function.h:387:20: note: 'const Eigen::Matrix<double, -1, 1>' is not derived from 'const std::move_iterator<_Iterator>' { return __x < __y; } ^ In file included from /usr/include/c++/5/bits/stl_algobase.h:67:0, from /usr/include/c++/5/bits/char_traits.h:39, from /usr/include/c++/5/ios:40, from /usr/include/c++/5/istream:38, from /usr/include/c++/5/sstream:38, from /usr/include/c++/5/complex:45, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Core:80, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Dense:1, from test.cpp:1: /usr/include/c++/5/bits/stl_iterator.h:1095:5: note: candidate: template<class _Iterator> bool std::operator<(const std::move_iterator<_Iterator>&, const std::move_iterator<_Iterator>&) operator<(const move_iterator<_Iterator>& __x, ^ /usr/include/c++/5/bits/stl_iterator.h:1095:5: note: template argument deduction/substitution failed: In file included from /usr/include/c++/5/string:48:0, from /usr/include/c++/5/bits/locale_classes.h:40, from /usr/include/c++/5/bits/ios_base.h:41, from /usr/include/c++/5/ios:42, from /usr/include/c++/5/istream:38, from /usr/include/c++/5/sstream:38, from /usr/include/c++/5/complex:45, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Core:80, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Dense:1, from test.cpp:1: /usr/include/c++/5/bits/stl_function.h:387:20: note: 'const Eigen::Matrix<double, -1, 1>' is not derived from 'const std::move_iterator<_Iterator>' { return __x < __y; } ^ In file included from /usr/include/c++/5/string:52:0, from /usr/include/c++/5/bits/locale_classes.h:40, from /usr/include/c++/5/bits/ios_base.h:41, from /usr/include/c++/5/ios:42, from /usr/include/c++/5/istream:38, from /usr/include/c++/5/sstream:38, from /usr/include/c++/5/complex:45, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Core:80, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Dense:1, from test.cpp:1: /usr/include/c++/5/bits/basic_string.h:4987:5: note: candidate: template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&, const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&) operator<(const basic_string<_CharT, _Traits, _Alloc>& __lhs, ^ /usr/include/c++/5/bits/basic_string.h:4987:5: note: template argument deduction/substitution failed: In file included from /usr/include/c++/5/string:48:0, from /usr/include/c++/5/bits/locale_classes.h:40, from /usr/include/c++/5/bits/ios_base.h:41, from /usr/include/c++/5/ios:42, from /usr/include/c++/5/istream:38, from /usr/include/c++/5/sstream:38, from /usr/include/c++/5/complex:45, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Core:80, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Dense:1, from test.cpp:1: /usr/include/c++/5/bits/stl_function.h:387:20: note: 'const Eigen::Matrix<double, -1, 1>' is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>' { return __x < __y; } ^ In file included from /usr/include/c++/5/string:52:0, from /usr/include/c++/5/bits/locale_classes.h:40, from /usr/include/c++/5/bits/ios_base.h:41, from /usr/include/c++/5/ios:42, from /usr/include/c++/5/istream:38, from /usr/include/c++/5/sstream:38, from /usr/include/c++/5/complex:45, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Core:80, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Dense:1, from test.cpp:1: /usr/include/c++/5/bits/basic_string.h:4999:5: note: candidate: template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&, const _CharT*) operator<(const basic_string<_CharT, _Traits, _Alloc>& __lhs, ^ /usr/include/c++/5/bits/basic_string.h:4999:5: note: template argument deduction/substitution failed: In file included from /usr/include/c++/5/string:48:0, from /usr/include/c++/5/bits/locale_classes.h:40, from /usr/include/c++/5/bits/ios_base.h:41, from /usr/include/c++/5/ios:42, from /usr/include/c++/5/istream:38, from /usr/include/c++/5/sstream:38, from /usr/include/c++/5/complex:45, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Core:80, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Dense:1, from test.cpp:1: /usr/include/c++/5/bits/stl_function.h:387:20: note: 'const Eigen::Matrix<double, -1, 1>' is not derived from 'const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>' { return __x < __y; } ^ In file included from /usr/include/c++/5/string:52:0, from /usr/include/c++/5/bits/locale_classes.h:40, from /usr/include/c++/5/bits/ios_base.h:41, from /usr/include/c++/5/ios:42, from /usr/include/c++/5/istream:38, from /usr/include/c++/5/sstream:38, from /usr/include/c++/5/complex:45, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Core:80, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Dense:1, from test.cpp:1: /usr/include/c++/5/bits/basic_string.h:5011:5: note: candidate: template<class _CharT, class _Traits, class _Alloc> bool std::operator<(const _CharT*, const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&) operator<(const _CharT* __lhs, ^ /usr/include/c++/5/bits/basic_string.h:5011:5: note: template argument deduction/substitution failed: In file included from /usr/include/c++/5/string:48:0, from /usr/include/c++/5/bits/locale_classes.h:40, from /usr/include/c++/5/bits/ios_base.h:41, from /usr/include/c++/5/ios:42, from /usr/include/c++/5/istream:38, from /usr/include/c++/5/sstream:38, from /usr/include/c++/5/complex:45, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Core:80, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Dense:1, from test.cpp:1: /usr/include/c++/5/bits/stl_function.h:387:20: note: mismatched types 'const _CharT*' and 'Eigen::Matrix<double, -1, 1>' { return __x < __y; } ^ In file included from /usr/include/c++/5/bits/ios_base.h:46:0, from /usr/include/c++/5/ios:42, from /usr/include/c++/5/istream:38, from /usr/include/c++/5/sstream:38, from /usr/include/c++/5/complex:45, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Core:80, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Dense:1, from test.cpp:1: /usr/include/c++/5/system_error:200:3: note: candidate: bool std::operator<(const std::error_code&, const std::error_code&) operator<(const error_code& __lhs, const error_code& __rhs) noexcept ^ /usr/include/c++/5/system_error:200:3: note: no known conversion for argument 1 from 'const Eigen::Matrix<double, -1, 1>' to 'const std::error_code&' /usr/include/c++/5/system_error:274:3: note: candidate: bool std::operator<(const std::error_condition&, const std::error_condition&) operator<(const error_condition& __lhs, ^ /usr/include/c++/5/system_error:274:3: note: no known conversion for argument 1 from 'const Eigen::Matrix<double, -1, 1>' to 'const std::error_condition&' In file included from /usr/include/c++/5/tuple:39:0, from /usr/include/c++/5/functional:55, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Core:262, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Dense:1, from test.cpp:1: /usr/include/c++/5/array:250:5: note: candidate: template<class _Tp, long unsigned int _Nm> bool std::operator<(const std::array<_Tp, _Nm>&, const std::array<_Tp, _Nm>&) operator<(const array<_Tp, _Nm>& __a, const array<_Tp, _Nm>& __b) ^ /usr/include/c++/5/array:250:5: note: template argument deduction/substitution failed: In file included from /usr/include/c++/5/string:48:0, from /usr/include/c++/5/bits/locale_classes.h:40, from /usr/include/c++/5/bits/ios_base.h:41, from /usr/include/c++/5/ios:42, from /usr/include/c++/5/istream:38, from /usr/include/c++/5/sstream:38, from /usr/include/c++/5/complex:45, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Core:80, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Dense:1, from test.cpp:1: /usr/include/c++/5/bits/stl_function.h:387:20: note: 'const Eigen::Matrix<double, -1, 1>' is not derived from 'const std::array<_Tp, _Nm>' { return __x < __y; } ^ In file included from /usr/include/c++/5/functional:55:0, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Core:262, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Dense:1, from test.cpp:1: /usr/include/c++/5/tuple:928:5: note: candidate: template<class ... _TElements, class ... _UElements> constexpr bool std::operator<(const std::tuple<_Elements ...>&, const std::tuple<_Elements ...>&) operator<(const tuple<_TElements...>& __t, ^ /usr/include/c++/5/tuple:928:5: note: template argument deduction/substitution failed: In file included from /usr/include/c++/5/string:48:0, from /usr/include/c++/5/bits/locale_classes.h:40, from /usr/include/c++/5/bits/ios_base.h:41, from /usr/include/c++/5/ios:42, from /usr/include/c++/5/istream:38, from /usr/include/c++/5/sstream:38, from /usr/include/c++/5/complex:45, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Core:80, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Dense:1, from test.cpp:1: /usr/include/c++/5/bits/stl_function.h:387:20: note: 'const Eigen::Matrix<double, -1, 1>' is not derived from 'const std::tuple<_Elements ...>' { return __x < __y; } ^ In file included from /usr/include/c++/5/vector:64:0, from /usr/include/c++/5/bits/random.h:34, from /usr/include/c++/5/random:49, from /usr/include/c++/5/bits/stl_algo.h:66, from /usr/include/c++/5/algorithm:62, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Core:269, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Dense:1, from test.cpp:1: /usr/include/c++/5/bits/stl_vector.h:1528:5: note: candidate: template<class _Tp, class _Alloc> bool std::operator<(const std::vector<_Tp, _Alloc>&, const std::vector<_Tp, _Alloc>&) operator<(const vector<_Tp, _Alloc>& __x, const vector<_Tp, _Alloc>& __y) ^ /usr/include/c++/5/bits/stl_vector.h:1528:5: note: template argument deduction/substitution failed: In file included from /usr/include/c++/5/string:48:0, from /usr/include/c++/5/bits/locale_classes.h:40, from /usr/include/c++/5/bits/ios_base.h:41, from /usr/include/c++/5/ios:42, from /usr/include/c++/5/istream:38, from /usr/include/c++/5/sstream:38, from /usr/include/c++/5/complex:45, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Core:80, from /home/alaya/.softwares/linear_algebra/eigen3.3/include/eigen3/Eigen/Dense:1, from test.cpp:1: /usr/include/c++/5/bits/stl_function.h:387:20: note: 'const Eigen::Matrix<double, -1, 1>' is not derived from 'const std::vector<_Tp, _Alloc>' { return __x < __y; } ^ make: *** [try] Error 1
I am using g ++ 5.4.0 and Eigen 3.3