Found the following significant warnings:
  sampler.cpp:107:45: warning: 'const arma::mtOp<unsigned int, T1, arma::op_sort_index> arma::sort_index(const arma::Base<typename T1::elem_type, T1>&, arma::uword) [with T1 = arma::Mat<double>; typename T1::elem_type = double; arma::uword = unsigned int]' is deprecated (declared at d:/RCompile/CRANpkg/lib/3.7/RcppArmadillo/include/armadillo_bits/fn_sort_index.hpp:43) [-Wdeprecated-declarations]
  sampler.cpp:108:28: warning: 'typename arma::enable_if2<(arma::is_arma_type<T1>::value && arma::resolves_to_vector<T1>::yes), const arma::Op<T1, arma::op_sort_vec> >::result arma::sort(const T1&, arma::uword) [with T1 = arma::Col<double>; typename arma::enable_if2<(arma::is_arma_type<T1>::value && arma::resolves_to_vector<T1>::yes), const arma::Op<T1, arma::op_sort_vec> >::result = const arma::Op<arma::Col<double>, arma::op_sort_vec>; arma::uword = unsigned int]' is deprecated (declared at d:/RCompile/CRANpkg/lib/3.7/RcppArmadillo/include/armadillo_bits/fn_sort.hpp:74) [-Wdeprecated-declarations]
  sampler.cpp:169:45: warning: 'const arma::mtOp<unsigned int, T1, arma::op_sort_index> arma::sort_index(const arma::Base<typename T1::elem_type, T1>&, arma::uword) [with T1 = arma::Mat<double>; typename T1::elem_type = double; arma::uword = unsigned int]' is deprecated (declared at d:/RCompile/CRANpkg/lib/3.7/RcppArmadillo/include/armadillo_bits/fn_sort_index.hpp:43) [-Wdeprecated-declarations]
  sampler.cpp:170:28: warning: 'typename arma::enable_if2<(arma::is_arma_type<T1>::value && arma::resolves_to_vector<T1>::yes), const arma::Op<T1, arma::op_sort_vec> >::result arma::sort(const T1&, arma::uword) [with T1 = arma::Col<double>; typename arma::enable_if2<(arma::is_arma_type<T1>::value && arma::resolves_to_vector<T1>::yes), const arma::Op<T1, arma::op_sort_vec> >::result = const arma::Op<arma::Col<double>, arma::op_sort_vec>; arma::uword = unsigned int]' is deprecated (declared at d:/RCompile/CRANpkg/lib/3.7/RcppArmadillo/include/armadillo_bits/fn_sort.hpp:74) [-Wdeprecated-declarations]
See 'd:/Rcompile/CRANpkg/local/3.7/markovchain.Rcheck/00install.out' for details.