anchor.diff:  
   uniform_walk(_Id, X, Y, P = #payload{pos_noise = N}) ->
     {
  -    X + math:sqrt(N) * uniform_noise(),
  -    Y + math:sqrt(N) * uniform_noise(),
  +    X + math:sqrt(12.0) * N * uniform_noise(),
  +    Y + math:sqrt(12.0) * N * uniform_noise(),
  +    P
  +  }.
  +
  +normal_walk(_Id, X, Y, P = #payload{pos_noise = N}) ->
  +  {
  +    X + math:sqrt(N) * normal_noise(),
  +    Y + math:sqrt(N) * normal_noise(),
       P
     }.
   
  
positive.code: 
  uniform_noise() ->
    random:uniform() - 0.5.
  
negative.code:          circular/4,
           linear/4,
           uniform_walk/4,
           normal_walk/4,
           compose/2
          ]).
  
  