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my @keys = qw( 0 0.1 0.3 1 3 10 30 1000 );
my %n;
for ( my $mag = 5.0 ; $mag < 9.0 ; $mag += 0.1 ) {
  @{ $n{ $mag } }{ @keys } = ( 0 ) x @keys;
}

  my @keys = qw(a b c d);
  my %hash; 
  @hash{@keys} = (1) x @keys;