my @matrix = (
   [ qw(ab cd ef gh)],
   [ qw(ij kl mn op)],
   [ qw(qr st uv wx)]
);

# should become
my @transposed = (
   [ qw(ab ij qr)],
   [ qw(cd kl st)],
   [ qw(ef mn uv)],
   [ qw(gh op wx)]
);