pi.sh


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#!/bin/sh

### pi.sh, https://en.wikipedia.org/wiki/Pi
# In 1706 John Machin used the Gregory–Leibniz series to produce an algorithm
# that converged much faster. Machin reached 100 digits of π with this
# formula. Other mathematicians created variants, now known as Machin-like
# formulae, that were used to set several successive records for calculating
# digits of π. Machin-like formulae remained the best-known method for
# calculating π well into the age of computers, and were used to set records
# for 250 years, culminating in a 620-digit approximation in 1946 by Daniel
# Ferguson–the best approximation achieved without the aid of a calculating
# device.

awk -v fig=${1} '
    function pi() {
        return 4*(4*atan2(1,5) - atan2(1,239))
    }
    BEGIN {
        if (fig <= 0)
            fig = 6
        str = "%." fig "g\n"
        printf(str, pi())
    }
'