Friday, April 12, 2013

My Pi chapter 2

Post 2

Something I forgot about initial setup: U.S. users -- be sure to change the default keyboard from UK to US. Otherwise, lots of luck finding important special characters.

Here's my Python program (copy/try it if you wish):
# Compute Pi to 10,000 places
# recoded using the algorithm from "ABC Programmers Handbook", Geurts, et al
def arccot(x, unity):
    sum = xpower = unity // x
    n = 3
    sign = -1
    while 1:
        xpower = xpower // (x*x)
        term = xpower // n
        if not term:
        sum += sign * term
        sign = -sign
        n += 2
    return sum

def pi(digits):
    unity = 10**(digits + 10)
    pi = 4 * (4*arccot(5, unity) - arccot(239, unity))
    return pi // 10**10

ans = str(pi(10000))
ans = ans[0:1]+'.'+ans[1:] # insert decimal point
print ans
BTW: this takes 4 seconds on the Pi and .6 second on my iMac. Same answer, though.

What I'd like to do with the Pi: (sounds like a 3rd-graders essay)
My grand-daughter & husband have a vegetable farm. They have built a cold storage building and need to trick a window AC unit into keeping it cooled to 40 degrees F. They also could use other automation aids: a) alarm on the lock, motion detector, soil moisture reading, plus lots more. I'd like them to be able to control the Pi via a local WAN by an iPhone. This will be a challenge!

More as I progress.

Dick Haight

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