teaching machines

Randomness in Madeup

October 13, 2014 by Chris Johnson. Filed under madeup, public.

About 30% into writing tests for a piece of code, my energy deflates. When I consider how many more tests I have to write to thoroughly test my code, I am overwhelmed. The worst part about testing is that you can’t just tax the moving parts of your software the way someone like you would. You have to step into the mind of your most incompetent user. I’m guessing criminal investigators face a similar problem when hunting down a homicidal maniac. Both of us have to twist our brain into thinking irrational and perverse thoughts to crack the case.

I then decide that the best thing for me to do is randomly generate a bunch of input data and see how my software handles it. That’s what I can do now in Madeup: generate random data. Two new constructs exist: a special seed variable and a random function:

seed = 10 -- chooses random sequence 10
n = random lo hi -- get a random number from [lo, hi]

If the seed is not set by the user, the current clock value is used.

I offer a few examples of random’s use.

Random Dots

A collection of randomly-placed and randomly-sized spheres.

nsides = 30

repeat 150
  radius = random 1 3
  x = random -10 10
  y = random -10 10
  z = random -10 10
  moveto x y z
end

dots

Random Top

A vertical 10-node tube with each node assigned a random radius.

moveto 0 0 0
seed = 10
nsides = 40
repeat 10
  radius = random 1 5
  move 1
end
tube

Random Strand

A strand generated from a random 3-D walk.

moveto 0 0 0
nsides = 10
radius = 4
seed = 27
repeat 300
  dimension = random 0 2
  angle = random 50 70
  if dimension == 0
    yaw angle
  else
    if dimension == 1
      pitch angle
    else
      roll angle
    end
  end
  move (random 1 3)
end
dots

Random Terrain

Rocky terrain generated by perturbing the nodes of a 50×50 grid by some random amount.

size = 50
seed = 60
for r to size
  for c to size
    moveto c r 0.5 * (random -1 1)
  end
end
surface size size