use strict;

my @bin_labels = qw( 0 0.1 0.3 1 3 10 30 1000 );

{
  my $step_size  = 0.1;
  my $start      = 5.0;
  my $finish     = 9.0;

  sub index_to_mag {
    my $i = shift;
    return $start + $i * $step_size;
  }

  sub mag_to_index {
    my $mag = shift;
    return sprintf "%.f", ($mag - $start) / $step_size;
  }
}

my @n;
for ( my $i = 0; $i < mag_to_index( 9.0 ); ++$i ) {
  $n[ $i ]{ $_ } = 0 for @bin_labels;
}

for ( my $mag = 5.5;
      $mag < 9.0;
      $mag = sprintf "%.1f", $mag + 0.1 ) {
  printf "%.1f %f\n", $mag, $n[ mag_to_index( $mag ) ]{ 30 };
}