eliminate the use of deprecated std::ptr_fun
std::ptr_fun has been deprecated in C++11, and will be removed in C++17 (see eg. http://en.cppreference.com/w/cpp/utility/functional/ptr_fun) This commit removes the one occurrence of it in PHYS
std::ptr_fun has been deprecated in C++11, and will be removed in C++17 (see eg. http://en.cppreference.com/w/cpp/utility/functional/ptr_fun) This commit removes the one occurrence of it in PHYS