input: Write a function to generate a Python program that adds two numbers and then doubles the result. If the given numbers are not provided, return 0.
  
  def double_add(num1=0, num2=0):
      return (num1 + num2) * 2
  
  assert double_add(3, 4) == 14
  assert double_add(0, 0) == 0
  assert double_add(1, 1) == 4
  assert double_add(-2, 2) == 0
  assert double_add() == 0
output: def double_add(num1=0, num2=0):
      return (num1 + num2) * 2