input: Write a function to add two matrices. If the matrices have different dimensions, return 'Matrices not compatible'. Otherwise, return the resulting matrix after adding corresponding elements.
  
  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]])==[[4], [6]]
  assert add_matrix([[1, 2], [3, 4]], [[5, 6], [7, 8], [9, 10]])=='Matrices not compatible'
  assert add_matrix([[1, 2], [3, 4]], [[5, 6, 7], [8, 9, 10]])=='Matrices not compatible'
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 [[a + b for a, b in zip(row1, row2)] for row1, row2 in zip(matrix1, matrix2)]