input: Write a function to generate a Python program that adds two numbers and then doubles the result. If the given inputs are integers or floats, return the doubled sum.
  assert double_add(3, 4)==14
  assert double_add(0, 0)==0
  assert double_add(-1, 1)==0
  assert double_add(2.5, 2.5)==10.0
  assert double_add(-3, -3)==-12
output: def double_add(a, b):
      return (a + b) * 2