bgneal@45: """Chapter 6, exercise 4 in Allen Downey's Think Complexity book.
bgneal@45: 
bgneal@45: The goal of this exercise is to implement a Turing machine.
bgneal@45: See http://en.wikipedia.org/wiki/Turing_machine.
bgneal@45: 
bgneal@45: 4. Write a class named TMDrawer that generates an image that represents the
bgneal@45:    state of the tape and the position and state of the head. For one example of
bgneal@45:    what that might look like, see
bgneal@45:    http://mathworld.wolfram.com/TuringMachine.html.
bgneal@45: 
bgneal@45: """
bgneal@45: import matplotlib.pyplot as pyplot
bgneal@45: import numpy
bgneal@45: 
bgneal@45: from CADrawer import Drawer
bgneal@45: 
bgneal@45: 
bgneal@45: class TMDrawer(Drawer):
bgneal@45:     """Implementation of Drawer using matplotlib for Turing Machines.
bgneal@45: 
bgneal@45:     We visualize the tape and machine head/state by drawing the tape state as
bgneal@45:     a row, then adding a row underneath that for the head & state. The tape head
bgneal@45:     is drawn as a solid square whose color represents the state.
bgneal@45: 
bgneal@45:     """
bgneal@45:     def __init__(self, tape_colors, state_colors, cmap=None):
bgneal@45:         self.tape_colors = tape_colors
bgneal@45:         self.state_colors = state_colors
bgneal@45:         self.cmap = cmap if cmap else 'spectral'
bgneal@45: 
bgneal@45:     def draw(self, tm, start=0, end=None):
bgneal@45:         """Draws the TM using pyplot.pcolor."""
bgneal@45:         tape = tm.get_array(start, end)
bgneal@45:         rows, cols = tape.shape
bgneal@45: 
bgneal@45:         # create a new array that has twice as many rows
bgneal@45:         steps = rows
bgneal@45:         rows *= 2
bgneal@45:         a = numpy.zeros((rows, cols), dtype=numpy.int8)
bgneal@45: 
bgneal@45:         # copy the tape state into the array at every other row
bgneal@45:         for i in xrange(steps):
bgneal@45:             for j in xrange(cols):
bgneal@45:                 #a[n, j] = self.tape_colors[tape[i, j]]
bgneal@45:                 c = self.tape_colors[tape[i, j]]
bgneal@45:                 a[i * 2, j] = c
bgneal@45: 
bgneal@45:         # copy the head position & state into every other row
bgneal@45:         n = 1
bgneal@45:         for pos, state in tm.history:
bgneal@45:             a[n, pos] = self.state_colors[state]
bgneal@45:             n += 2
bgneal@45: 
bgneal@45:         # flipud puts the first row at the top;
bgneal@45:         pyplot.pcolor(numpy.flipud(a), cmap=self.cmap)
bgneal@45:         pyplot.axis([0, cols, 0, rows])
bgneal@45:         pyplot.colorbar()
bgneal@45: 
bgneal@45:         # empty lists draw no ticks
bgneal@45:         pyplot.xticks([])
bgneal@45:         pyplot.yticks([])
bgneal@45: 
bgneal@45:     def show(self):
bgneal@45:         """display the pseudocolor representation of the CA"""
bgneal@45:         pyplot.show()
bgneal@45: 
bgneal@45:     def save(self, filename='tm.png'):
bgneal@45:         """save the pseudocolor representation of the TM in (filename)."""
bgneal@45:         pyplot.savefig(filename)
bgneal@45: