input: Write a python function to calculate the sum of all elements in a 2D matrix.
  assert calculate_matrix_sum([[1, 2, 3], [4, 5, 6], [7, 8, 9]]) == 45
  assert calculate_matrix_sum([[0, 0, 0], [0, 0, 0], [0, 0, 0]]) == 0
  assert calculate_matrix_sum([[1, -1], [1, -1], [1, -1]]) == 0
output: def calculate_matrix_sum(matrix):
      return sum(sum(row) for row in matrix)