ary = [3, 5, 13, 12, 0]

# Regular sort, then reverse
ary.sort.reverse
# => [13, 12, 5, 3, 0]

# Descending-order sort using a Schwartzian transform
ary.sort_by { |x| -x }
# => [13, 12, 5, 3, 0]

# Descending-order sort using map and sort
ary.map { |x| -x }.sort.map { |x| -x}
# => [13, 12, 5, 3, 0]