input: Write a function to add two matrices. The function should check if the matrices are of the same size (same number of rows and columns). If they are compatible, it should return the result of the addition of the two matrices. If not, it should return a message stating that the matrices are not compatible.
  
  def add_matrix(matrix1, matrix2):
      if len(matrix1) != len(matrix2):
          return 'Matrices not compatible'
      if len(matrix1[0]) != len(matrix2[0]):
          return 'Matrices not compatible'
      
      rows = len(matrix1)
      cols = len(matrix1[0])
      result = [[sum(row) for row in zip(*size)] for size in zip(matrix1, matrix2)]
      
      return result
  
  assert add_matrix([[1, 2], [3, 4]], [[2, 3], [4, 5]]) == [[3, 5], [7, 9]]
  assert add_matrix([[1, 2], [3, 4]], [[5, 6]]) == 'Matrices not compatible'
  assert add_matrix([[1, 2]], [[3], [4]]) == 'Matrices not compatible'
  assert add_matrix([[1, 2, 3], [4, 5, 6]], [[7, 8, 9], [10, 11, 12]]) == [[8, 10, 12], [14, 16, 18]]
output: def add_matrix(matrix1, matrix2):
      if len(matrix1) != len(matrix2) or len(matrix1[0]) != len(matrix2[0]):
          return 'Matrices not compatible'
      
      result = [[matrix1[i][j] + matrix2[i][j] for j in range(len(matrix1[0]))] for i in range(len(matrix1))]
      
      return result