Mueller's convergence

iter-oe.raku

#!/usr/bin/env raku
# Mueller's convergence, from p. 14 of
# https://people.eecs.berkeley.edu/~wkahan/Mindless.pdf

constant x0 = 4.FatRat;
constant x1 = (4.25).FatRat;

sub MAIN(Int $n) {
	say iter-oe $n;
}

sub oe(FatRat $y, FatRat $z --> FatRat) {
	108.0 - ( 815.0 - 1500.0 / $z ) / $y 
}

sub iter-oe(Int $n --> FatRat) {
	do given $n {
		when 0  { x0 }
		when 1  { x1 }
		when 2  { oe( x1,            x0 ) }
		when 3  { oe( iter-oe(2),    iter-oe(1) ) }
		default { oe( iter-oe($n-1), iter-oe($n-2) ) }
	}
}