input: Write a function to add two matrices. The function should return the resulting matrix if the dimensions of the two matrices are compatible. If the dimensions are not compatible, the function should return 'Matrices not compatible'.
  
  
  assert add_matrix([[1, 2], [3, 4]], [[5, 6], [7, 8]]) == [[6, 8], [10, 12]]
  assert add_matrix([[1, 2, 3], [4, 5, 6]], [[1, 2, 3], [4, 5, 6]]) == [[2, 4, 6], [8, 10, 12]]
  assert add_matrix([[1, 2], [3, 4]], [[1, 2, 3], [4, 5, 6]]) == 'Matrices not compatible'
  assert add_matrix([[1, 2]], [[3, 4]]) == [[4, 6]]
  assert add_matrix([[1]], [[2]]) == [[3]]
  
output: def add_matrix(matrix1, matrix2):
      if len(matrix1) != len(matrix2) or any(len(row1) != len(row2) for row1, row2 in zip(matrix1, matrix2)):
          return 'Matrices not compatible'
      return [[matrix1[i][j] + matrix2[i][j] for j in range(len(matrix1[0]))] for i in range(len(matrix1))]