Pi on a Pi for Pi Day

Calculating Pi on a Pi

Here’s a quick and dirty post for Pi Day which uses Python code by David Bau (http://davidbau.com/archives/2010/03/14/python_pipy_spigot.html) to compute pi to an arbitrary number of digits. The code implements a “spigot algorithm” developed by Jeremy Gibbons (http://www.cs.ox.ac.uk/people/jeremy.gibbons/publications/spigot.pdf). This algorithm can generate the nth digit of pi independently from the preceding digits and runs O(n) in time.

In honor of Pi Day, I ran the code on a Raspberry Pi 3. I slightly modified the calling function to write the generated digits to files in batches of 10000. The computations get slower as the decimal place gets larger. I didn’t time the code exactly, but the time stamps on the files written indicate the first 10000 digits took less than 1 minute, the next 10000 took approximately 2 minutes, then 4 minutes, 6 minutes, 8 minutes, 12 minutes, etc…

Sure you could find and download pi from some online source, but it’s much more fun to do it yourself. I’m running it on my Raspberry Pi 3 right now, and plan to write a another quick and dirty project by tomorrow display them in some way for Pi Day.

Modified source code is below (original code on David Bau’s blog)

#Pi digit generator function
def pi_decimal_digits():
  q, r, t, j = 1, 180, 60, 2
  while True:
    u, y = 3*(3*j+1)*(3*j+2), (q*(27*j-12)+5*r)//(5*t)
    yield y
    q, r, t, j = 10*q*j*(2*j-1), 10*u*(q*(5*j-2)+r-y*t), t*u, j+1

#Caller program writes digits to disk in batches of 10000
count, digits = 0, pi_decimal_digits()
n_per_file = 10000
while 1:
  fn = "pidigits_" + str(count+1) + "_to_" + str(count + n_per_file) + ".txt"
  f = open(fn, 'w')
  print "at " + str(count)
  with open(fn, 'w') as f:
    for j in xrange(n_per_file):
  count += n_per_file


YAWP – Yet Another Wall Plotter

 The Inspiration:

I’ve been very slow to create posts these last few months.  I like to think it’s not due to laziness, but just that I’ve been so busy playing with other projects.  I’m pushing myself to write up the more interesting ones.  These days I’ve been obsessed with machines that draw.  The biggest of these projects has been my wall plotter, nicknamed YAWP (Yet Another Wall Plotter).

A wall plotter (also known as V-plotter or polargraph) works by moving a pen around a vertical (or slightly angled) drawing surface by means of two motors attached to string or a timing belt.  Although wall plotters are really just very slow, low resolution printers, the potentially unlimited scalability and numerous variations in the output make them compelling to watch.  Because of their simple design and because it’s fun to watch a machine drawing with a pen, they are far more engaging than a typical desktop printer.

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