>perl -wMstrict -le
"use List::Util      qw(min);
 use List::MoreUtils qw(indexes);
 ;;
 my %matrix  = ( NI => [ 1, 5, 1, 3, 4 ] );
 ;;
 my @indices = do {
   my $array_ref = $matrix{NI};
   my $mat_min = min @$array_ref;
   indexes { $_ == $mat_min } @$array_ref;
   };
 print qq{(@indices)};
"
(0 2)