input: Write a python function to calculate the sum of all elements in a 2D array.
  assert calculate_sum([[1, 2, 3], [4, 5, 6], [7, 8, 9]]) == 45
  assert calculate_sum([[10, 20], [30, 40]]) == 100
  assert calculate_sum([[1, 1, 1], [1, 1, 1], [1, 1, 1]]) == 9
output: def calculate_sum(matrix):
      return sum(sum(row) for row in matrix)