input: Write a python function to assign variables from a matrix.
  assert assign_variables([[1, 2, 3], [4, 5, 6], [7, 8, 9]]) == [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
  assert assign_variables([[10, 20], [30, 40], [50, 60]]) == [[10, 20], [30, 40], [50, 60]]
  assert assign_variables([[1], [2], [3]]) == [[1], [2], [3]]
output: def assign_variables(matrix):
      return matrix