python计算的实际pi值不正确

Question

我的代码输出的pi值不正确...

#!/usr/bin/python

import sys
import gmpy2
from gmpy2 import mpfr

n = int(sys.argv[1])
l = int(sys.argv[2])

gmpy2.get_context().precision = n * 4

p0 = mpfr(1)
q0 = mpfr(1)
t0 = mpfr(0)

p = mpfr(0)
q = mpfr(0)
t = mpfr(0)
a = mpfr(0)

for loop in range(1, l+1, 1):
    p = (2*loop - 1)*(6*loop - 1)*(6*loop - 5)
    q = (loop**3)*(640320**3)/24
    a = (13591409 + 545140134*loop)
    if loop % 2 == 0:
        a = -1 * a
    else:
        a = 1 * a

    t = t0*q + a*p

    p = p*p0
    q = q*q0

    p0 = p
    q0 = q
    t0 = t

pi = 640320 * gmpy2.sqrt(640320)*q
pi = pi/(12*(t + 13591409*q))

print(pi)

我认为我的算法是正确的。只是为了确定，如果不正确，请告诉我。

3.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170679821480865132823066486

预期输出：

{{1}}