input: Write a function to initialize a matrix by adding corresponding elements of two matrices.
  assert initialize_matrix([[1, 2], [3, 4]], [[5, 6], [7, 8]]) == [[6, 8], [10, 12]]
  assert initialize_matrix([[0, 0], [0, 0]], [[1, 1], [1, 1]]) == [[1, 1], [1, 1]]
  assert initialize_matrix([[1, 2, 3], [4, 5, 6]], [[7, 8, 9], [10, 11, 12]]) == [[8, 10, 12], [14, 16, 18]]
output: def initialize_matrix(matrix1, matrix2):
      return [[matrix1[i][j] + matrix2[i][j] for j in range(len(matrix1[0]))] for i in range(len(matrix1))]