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Create a circular cellular automaton for ch 6, exercise 1.
author Brian Neal <bgneal@gmail.com>
date Sat, 12 Jan 2013 15:03:31 -0600
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children 039249efe42f
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39:49db586c727a 40:ae310a2f42b4
1 """Chapter 6, exercise 1 in Allen Downey's Think Complexity book.
2
3 "Create a new class called CircularCA that extends CA so that the cells are
4 arranged in a ring. Hint: you might find it useful to add a column of 'ghost
5 cells' to the array."
6
7 """
8
9 import numpy
10
11 from CA import CA
12
13
14 class CircularCA(CA):
15 """A circular cellular automaton; the cells are arranged in a ring."""
16
17 def __init__(self, rule, n=100, ratio=2):
18 """Parameters:
19
20 * rule: an integer in the range 0-255 that represents the CA rule
21 using Wolfram's encoding
22 * n: the number of rows (time steps) in the result
23 * ratio: the ratio of columns to rows
24
25 """
26 self.table = self.make_table(rule)
27 self.n = n
28 # a ghost column is added to either end
29 self.m = ratio * n + 3 # add 2 ghost columns
30 self.array = numpy.zeros((n, self.m), dtype=numpy.int8)
31 self.next = 0
32
33 def start_single(self):
34 self.array[0, 1] = 1
35 self.next = 1
36
37 def step(self):
38 """Executes one time step by computing the next row of the array."""
39 i = self.next
40 self.next += 1
41 assert i > 0, 'call start_single() or start_random() first'
42
43 a = self.array
44 t = self.table
45
46 # update the ghost cells to enable wrapping
47 a[i - 1, 0] = a[i - 1, self.m - 2]
48 a[i - 1, self.m - 1] = a[i - 1, 1]
49
50 for j in xrange(1, self.m - 1):
51 a[i, j] = t[tuple(a[i - 1, j-1:j+2])]
52
53
54 def get_array(self, start=0, end=None):
55 """Gets a slice of columns from the CA, with slice indices
56 (start, end).
57
58 """
59 # do not return the ghost columns
60 if end==None:
61 return self.array[:, start+1:self.m-1]
62 else:
63 return self.array[:, start+1:end+1]
64
65
66 if __name__ == '__main__':
67
68 import sys
69 from CADrawer import PyplotDrawer
70
71 def main(script, rule, n):
72 rule = int(rule)
73 n = int(n)
74 ca = CircularCA(rule, n)
75 ca.start_single()
76 ca.loop(n - 1)
77
78 drawer = PyplotDrawer()
79 drawer.draw(ca)
80 drawer.show()
81
82
83 main(*sys.argv)