Compute π with an infinite series

pi_infinite_series

def f(n) 
  (2 * n + 1)**-1
end

def g(n)
  ((-1)**n).to_f
end


def pi
  0.upto(100000).inject(0) do |sum, n|
    sum + f(n) * g(n)
  end * 4
end


p 0.upto(10).map{|n| f(n) }
p 0.upto(10).map{|n| g(n) }

puts pi