Hi, the following code ``` #include <iostream> #include <Eigen/Core> using namespace Eigen; using myMatrix=Matrix<std::complex<double>, Eigen::Dynamic, Eigen::Dynamic, Eigen::RowMajor>; int main(int argc, char* argv[]){ myMatrix mat = myMatrix::Random(2,2); const auto m1 = mat.adjoint() * mat; const myMatrix m2 = mat.adjoint() * mat; std::cout << "m1 = \n" << m1 << std::endl; std::cout << "m2 = \n" << m2 << std::endl; std::cout << "diff=\n" << m1-m2 << std::endl; } ``` gives wrong results (m1-m2 != 0) when compiled with ```g++ -O3 -ffast-math ``` It works if ``-ffast-math`` is disabled. It also works for ``Eigen::ColMajor``. What I don't understand is that the wrong result also occurs when enabling MKL (``-DEIGEN_USE_MKL_ALL``). Compiling the code with clang or with icpc (using ``-fast`` as option) does not lead to errors. My g++ is ``` g++ (Arch Linux 9.2.1+20200130-2) 9.2.1 20200130 Copyright (C) 2019 Free Software Foundation, Inc. ``` I'm using Eigen commit ``a45d28256d020a4e871267c9bf00206fe9d2265e`` (Fri Jan 10, 2020)