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Generalized Sandpiles

Sandpiles are a very interesting construct to play with. Guided by 2 simple rules, they make for fun (noticed the alliteration?) visualizations.

Here are the vanilla sandpile rules:

  1. You have a grid of blocks (may or may not be a square). Each square in the grid can hold maximum of 3 sand particles.

  2. When any grid exceeds 3 sand particles, they topple

This happens forever until we have a stable sandpile. Pretty neat eh?

Generalized sandpiles

In this project, I have generalized the maximum that any square can hold. So, you can choose the maximum for any one square to be say, 10 while everone else is at 3.

This can make for some pretty graphics when done on a large sandpile.

$ pip install sandpiles

Demo visualization

Gifs

The gif above is created with 100 grains on the four corners of a 6x12 board. It ran for 29 iterations before stabilizing.

In [1]: from sandpiles.visualize import sandpile, run_pile, create_gif

In [2]: pile = sandpile(size="6x12", initial_max=0, initial_min=0)

In [3]: pile[(1, 12)]["#"] = 100

In [4]: pile[(6, 1)]["#"] = 100

In [5]: pile[(6, 12)]["#"] = 100

In [6]: pile[(1, 1)]["#"] = 100

In [7]: run_pile(pile, picture=False, gif=True)
Created sandpiles.gif
Ran for 29 iterations

Images

Use it like so:

In [1]: from sandpiles.visualize import sandpile, run_pile

# creating an empty 30x100 grid
In [2]: pile = sandpile(size="30x100", initial_max=0, initial_min=0)

# adding 10,000 grains at bottom center square
In [3]: pile[(30, 50)]["#"] = 10000

# simulating the pile
In [4]: run_pile(pile, save=True)
Ran for 3644 iterations

In [5]: !ls sandpile.png
sandpile.png

The script will produce this image

img

or print labels too:

In [1]: pile = sandpile(size="10x50", initial_max=10, initial_min=10)
In [2]: run_pile(pile, labels=True)
Ran for 139 iterations

img

Implementation details

sandpile definition

Define a sandpile by giving the dimensions and characteristics of the grid. The max of each square in the grid is chosen by random and lies between sand_min and sand_max. The initial sand grains on each square are chosen randomly too and lie between initial_min and initial_max

sandpile argument signature:

sandpile(size="3x3", sand_min=3, sand_max=3, initial_min=10, initial_max=10):

Also, run_pile can print labels on the image if required run_pile argument signature:

run_pile(pile, save=False, labels=False):

pile structure

  • The primary data structure used is the pile hashtable (python dict). It is 1-indexed, and has the following structure:
In [1]: pile = sandpile(size="2x2")

In [2]: pile
Out[2]:
defaultdict(dict,
            {'c': 2,
             'r': 2,
             (1, 1): {'#': 10, 'max': 3},
             (1, 2): {'#': 10, 'max': 3},
             (2, 1): {'#': 10, 'max': 3},
             (2, 2): {'#': 10, 'max': 3}})

So, each square in the grid has 2 parameters -

  • # --> the number of sand grains on that square
  • max --> the maximum number of grains that square can hold, after which it topples

Toppling order

Since the maximum for any square is not 3 but can be decided by the user, I have defined a clockwise toppling order for each square.

That means, if any square has a "max" of 2, and "#" is 3; it will topple the first grain to the square on it's left, then the one above it, next to the one to it's right. It cannot topple to the one below it because it has no more grains left now.

Inspired by this amazing video - https://www.youtube.com/watch?v=1MtEUErz7Gg