input: Write a function to compute the average of the elements in a 2-dimensional array. The function should return the average value of all elements in the matrix.
  
  def averageMatrix(matrix):
      total_sum = 0
      num_elements = 0
      for row in matrix:
          for e in row:
              total_sum += e
              num_elements += 1
      return total_sum / num_elements
  
  a = [[3,2,6],
       [8,5,9],
       [4,7,1]]
  
  assert averageMatrix(a) == 4.777777777777778
  assert averageMatrix([[1, 2], [3, 4]]) == 2.5
  assert averageMatrix([[0]]) == 0
  assert averageMatrix([[10, 20, 30], [40, 50, 60]]) == 35.0
  assert averageMatrix([]) == 0
output: def averageMatrix(matrix):
      if not matrix:
          return 0
      total_sum = 0
      num_elements = 0
      for row in matrix:
          for e in row:
              total_sum += e
              num_elements += 1
      return total_sum / num_elements