input: Write a function to print the absolute difference between two given numbers. The function should take two parameters and return the absolute difference. If either number is negative, the function should still return the absolute difference.
  assert absolute_difference(-9, 5)==14
  assert absolute_difference(9, -5)==14
  assert absolute_difference(9, 5)==4
  assert absolute_difference(-9, -5)==4
  assert absolute_difference(0, 0)==0
output: def absolute_difference(a, b):
      return abs(a - b)