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Eigen::ArrayXd sort_vec(Eigen::ArrayXXd & arr, ArrayXd & sorted_arr) { Eigen::ArrayXd ind=ArrayXd::LinSpaced(arr.size(), 0, arr.size()-1); auto rule=[arr](int i, int j) -> bool{return arr(i)>arr(j);}; std::sort(ind.data(), ind.data()+ind.s

Ref https://forum.kde.org/viewtopic.php?t=112142 Code #include <iostream> #include <Eigen/Dense> using namespace Eigen; double my_atan2(double a, double b) { return std::atan2(a,b); } int main() { Matrix4d A, B, C; C = A.binaryExpr(B, std