Pick out the even (i,j where both even) elements from a matrix m[0::2, 0::2] // Numpy m(0::2, 0::2) // Fo

Pick out the even (i,j where both even) elements from a matrix m[0::2, 0::2] // Numpy m(0::2, 0::2) // Fortran [1] m(seq(0, last, 2), seq(0, last, 2)) // C++ Eigen [1] If you have declared the array to start indexing from 0.