Calculate Pi

Discussion in 'iOS Programming' started by xcodeNewbie, Jul 12, 2011.

  1. macrumors member

    Joined:
    Jul 1, 2011
    #1
    I want to make an app that calculates pi to any decimal place, even 1,000,000. I don't care how long it takes the computer. I know the formula for pi is as follows:
    pi / 4 = 4 * tan-1(1 / 5) - tan-1(1 / 239)
    However, I am at a loss of how to do this.
     
  2. macrumors 65816

    jiminaus

    Joined:
    Dec 16, 2010
    Location:
    Sydney
    #2
    You won't be able to use the standard C types such as double for this. You'll need an arbitrary-precision library like the GNU MP library http://gmplib.org/.

    Have you search for code to do this? Surely it's been done before?
     
  3. chown33, Jul 12, 2011
    Last edited: Jul 12, 2011

    macrumors 603

    Joined:
    Aug 9, 2009
    #3
    Using that formula, you'd first have to figure out how to calculate arctangents to arbitrarily long precision.

    You might be better off using a series that converges to pi. Example google search terms:
    pi series
    pi convergent series

    And the first step is probably to read the Wikipedia article on pi, which mentions series and even gives a simple example (Gregory series), which converges very slowly:
    http://en.wikipedia.org/wiki/Pi

    Also see:
    http://en.wikipedia.org/wiki/Approximations_of_π
     
  4. macrumors 68000

    Loge

    Joined:
    Jun 24, 2004
    Location:
    England
    #4

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