input: Write a function to add two matrices. If the matrices are not of the same size, return 'Matrices not compatible'. Otherwise, return the resulting matrix by adding corresponding elements of the input matrices.
  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]], [[5, 6], [7, 8]]) == [[6, 8], [10, 12]]
  assert add_matrix([[1, 2]], [[3, 4]]) == [[4, 6]]
  assert add_matrix([[1, 2], [3, 4]], [[1, 2, 3], [4, 5, 6]]) == 'Matrices not compatible'
  assert add_matrix([], []) == []
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