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From: tstorm@vu44.UUCP (Theo van der Storm)
Newsgroups: net.math
Subject: Re: Calculating Pi to Excessive Accuracy
Message-ID: <680@vu44.UUCP>
Date: Sat, 3-Aug-85 11:44:57 EDT
Article-I.D.: vu44.680
Posted: Sat Aug  3 11:44:57 1985
Date-Received: Sun, 4-Aug-85 06:31:33 EDT
References: <423@ist.UUCP>
Reply-To: tstorm@vu44.UUCP
Distribution: net
Organization: VU Informatica, Amsterdam
Lines: 51

In article <423@ist.UUCP> bco@ist.UUCP (Brian Collins) writes:
>Following Ken Yap's posting, which soaks up 2 hours of CPU to
>calculate Pi to 1000 decimal places, may I offer the
>following sh/bc script that takes just over 6 mins on my
>Pyramid.
>
>bc <<!
>	/* Computes Pi to $1 places */
>	t = 3 * 10^${1-100}
>	for (i = 1; t != 0; i++) {
>		p = p + t
>		t = t * (2 * i - 1) * (2 * i - 1) / (8 * i * (2 * i + 1))
>	}
>	p
>!
>
>	...differential of asin( x) ;	asin( 0.5) = 	pi / 6 ...
>
>Any advance on 6 minutes?
>
>Brian Collins		...mcvax!ist!bco (bco@ist)
>Imperial Software Technology, London

Using Ken Yap's formula (!) here is a bc program
(written by me), which is almost twice as fast as YOUR program:
[Replace =+, =/, etc. by +=, /=, etc. if necessary]

bc << EOF
n = $1
t = 16 * (10^n) / 5
e = 1
s = 0
while (t != 0){
    s =+ t / e
    t =/ -25
    e =+ 2
}
t = 4 * (10^n) / 239
e = 1
while (t != 0){
    s =- t / e
    t =/ -57121
    e =+ 2
}
s

Apparently, Ken Yap's implementation was not very efficient :-)
-- 
	Theo van der Storm,    052 19'08"N / 004 51'16"E
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