input: Write a python function to compute the sum of elements in an array.
  assert compute_sum([1, 2, 3, 4, 5]) == 15
  assert compute_sum([10, 20, 30]) == 60
  assert compute_sum([0, 0, 0, 0]) == 0
  assert compute_sum([-1, 1, -2, 2]) == 0
output: def compute_sum(arr):
      return sum(arr)