bgneal@40: """Chapter 6, exercise 1 in Allen Downey's Think Complexity book.
bgneal@40: 
bgneal@40: "Create a new class called CircularCA that extends CA so that the cells are
bgneal@40: arranged in a ring. Hint: you might find it useful to add a column of 'ghost
bgneal@40: cells' to the array."
bgneal@40: 
bgneal@40: """
bgneal@40: 
bgneal@40: import numpy
bgneal@40: 
bgneal@40: from CA import CA
bgneal@40: 
bgneal@40: 
bgneal@40: class CircularCA(CA):
bgneal@40:     """A circular cellular automaton; the cells are arranged in a ring."""
bgneal@40: 
bgneal@42:     def __init__(self, rule, n=100, m=50):
bgneal@40:         """Parameters:
bgneal@40: 
bgneal@40:         * rule: an integer in the range 0-255 that represents the CA rule
bgneal@40:         using Wolfram's encoding
bgneal@40:         * n: the number of rows (time steps) in the result
bgneal@42:         * m: the number of columns
bgneal@40: 
bgneal@40:         """
bgneal@40:         self.table = self.make_table(rule)
bgneal@40:         self.n = n
bgneal@40:         # a ghost column is added to either end
bgneal@42:         self.m = m + 2      # add 2 ghost columns
bgneal@40:         self.array = numpy.zeros((n, self.m), dtype=numpy.int8)
bgneal@40:         self.next = 0
bgneal@40: 
bgneal@40:     def start_single(self):
bgneal@40:         self.array[0, 1] = 1
bgneal@40:         self.next = 1
bgneal@40: 
bgneal@40:     def step(self):
bgneal@40:         """Executes one time step by computing the next row of the array."""
bgneal@40:         i = self.next
bgneal@40:         self.next += 1
bgneal@40:         assert i > 0, 'call start_single() or start_random() first'
bgneal@40: 
bgneal@40:         a = self.array
bgneal@40:         t = self.table
bgneal@40: 
bgneal@40:         # update the ghost cells to enable wrapping
bgneal@40:         a[i - 1, 0] = a[i - 1, self.m - 2]
bgneal@40:         a[i - 1, self.m - 1] = a[i - 1, 1]
bgneal@40: 
bgneal@40:         for j in xrange(1, self.m - 1):
bgneal@40:             a[i, j] = t[tuple(a[i - 1, j-1:j+2])]
bgneal@40: 
bgneal@42:     def loop(self, steps=1):
bgneal@42:         """Executes the given number of time steps."""
bgneal@42:         for i in xrange(steps):
bgneal@42:             self.step()
bgneal@40: 
bgneal@40:     def get_array(self, start=0, end=None):
bgneal@40:         """Gets a slice of columns from the CA, with slice indices
bgneal@40:         (start, end).
bgneal@40: 
bgneal@40:         """
bgneal@40:         # do not return the ghost columns
bgneal@40:         if end==None:
bgneal@40:             return self.array[:, start+1:self.m-1]
bgneal@40:         else:
bgneal@40:             return self.array[:, start+1:end+1]
bgneal@40: 
bgneal@42:     def wrap(self):
bgneal@42:         """Copies the last row to row 0, then resets the CA to start back at the
bgneal@42:         top.
bgneal@42: 
bgneal@42:         """
bgneal@42:         a = self.array
bgneal@42:         a[0, :] = a[self.next - 1, :]
bgneal@42:         self.next = 1
bgneal@42: 
bgneal@40: 
bgneal@40: if __name__ == '__main__':
bgneal@40: 
bgneal@40:     import sys
bgneal@40:     from CADrawer import PyplotDrawer
bgneal@40: 
bgneal@42:     def main(script, rule, n, m):
bgneal@40:         rule = int(rule)
bgneal@40:         n = int(n)
bgneal@42:         m = int(m)
bgneal@42:         ca = CircularCA(rule, n, m)
bgneal@40:         ca.start_single()
bgneal@40:         ca.loop(n - 1)
bgneal@40: 
bgneal@40:         drawer = PyplotDrawer()
bgneal@40:         drawer.draw(ca)
bgneal@40:         drawer.show()
bgneal@40: 
bgneal@40: 
bgneal@40:     main(*sys.argv)