Serious Pi Calculations
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Serious Pi Calculations

based on Ramanujan and the Chudnovsky brothers

Started Jan 18, 2021, struggling since
IOR 853

I have been happy with Machin's method for years -
- Simple theory and simple extended precision arithmetic. Good for my limited goals :-)
- Multipliers and divisors can fit into one computer "word" :-)
- Multiplicands and dividends can be as long as desired with simple processing.)
But, unfortunately a million decimal digits of accuracy can take 1/2 hour, (year 2020 INTEL processor) with computer time increasing as the square of the accuracy.)

In the early 1900s, Ramanujan developed a much faster converging series, and in the late 1900s the Chudnovsky brothers modified Ramanujan work to better fit computer calculations - used in all of the current huge accuracies.
Some comments from Ron Mak in 2019 and 2020

********** break

100 mpmath one-liners for pi
stolen from https://fredrikj.net/blog/2011/03/100-mpmath-one-liners-for-pi/ - on March 7, 2021

fredrikj.net / blog /

100 mpmath one-liners for pi

March 14, 2011

Since it’s pi day today, I thought I’d share a list of mpmath one-liners for computing the value of pi to high precision using various representations in terms of special functions, infinite series, integrals, etc. Most of them can already be found as doctest examples in some form in the mpmath documentation.

A few of the formulas explicitly involve pi. Using those to calculate pi is rather circular (!), though a few of them could still be used for computing pi using numerical root-finding. In any case, most of the formulas are circular even when pi doesn’t appear explicitly since mpmath is likely using its value internally. In any further case, the majority of the formulas are not efficient for computing pi to very high precision (at least as written). Still, ~50 digits is no problem. Enjoy!

from mpmath import *
mp.dps = 50; mp.pretty = True

+pi
180*degree
4*atan(1)
16*acot(5)-4*acot(239)
48*acot(49)+128*acot(57)-20*acot(239)+48*acot(110443)
chop(2*j*log((1-j)/(1+j)))
chop(-2j*asinh(1j))
chop(ci(-inf)/1j)
gamma(0.5)**2
beta(0.5,0.5)
(2/diff(erf, 0))**2
findroot(sin, 3)
findroot(cos, 1)*2
chop(-2j*lambertw(-pi/2))
besseljzero(0.5,1)
3*sqrt(3)/2/hyp2f1((-1,3),(1,3),1,1)
8/(hyp2f1(0.5,0.5,1,0.5)*gamma(0.75)/gamma(1.25))**2
4*(hyp1f2(1,1.5,1,1) / struvel(-0.5, 2))**2
1/meijerg([[],[]], [[0],[0.5]], 0)**2
(meijerg([[],[2]], [[1,1.5],[]], 1, 0.5) / erfc(1))**2
(1-e) / meijerg([[1],[0.5]], [[1],[0.5,0]], 1)
sqrt(psi(1,0.25)-8*catalan)
elliprc(1,2)*4
elliprg(0,1,1)*4
2*agm(1,0.5)*ellipk(0.75)
(gamma(0.75)*jtheta(3,0,exp(-pi)))**4
cbrt(gamma(0.25)**4*agm(1,sqrt(2))**2/8)
sqrt(6*zeta(2))
sqrt(6*(zeta(2,3)+5./4))
sqrt(zeta(2,(3,4))+8*catalan)
exp(-2*zeta(0,1,1))/2
sqrt(12*altzeta(2))
4*dirichlet(1,[0,1,0,-1])
2*catalan/dirichlet(-1,[0,1,0,-1],1)
exp(-dirichlet(0,[0,1,0,-1],1))*gamma(0.25)**2/(2*sqrt(2))
sqrt(7*zeta(3)/(4*diff(lerchphi, (-1,-2,1), (0,1,0))))
sqrt(-12*polylog(2,-1))
sqrt(6*log(2)**2+12*polylog(2,0.5))
chop(root(-81j*(polylog(3,root(1,3,1))+4*zeta(3)/9)/2,3))
2*clsin(1,1)+1
(3+sqrt(3)*sqrt(1+8*clcos(2,1)))/2
root(2,6)*sqrt(e)/(glaisher**6*barnesg(0.5)**4)
nsum(lambda k: 4*(-1)**(k+1)/(2*k-1), [1,inf])
nsum(lambda k: (3**k-1)/4**k*zeta(k+1), [1,inf])
nsum(lambda k: 8/(2*k-1)**2, [1,inf])**0.5
nsum(lambda k: 2*fac(k)/fac2(2*k+1), [0,inf])
nsum(lambda k: fac(k)**2/fac(2*k+1), [0,inf])*3*sqrt(3)/2
nsum(lambda k: fac(k)**2/(phi**(2*k+1)*fac(2*k+1)), [0,inf])*(5*sqrt(phi+2))/2
nsum(lambda k: (4/(8*k+1)-2/(8*k+4)-1/(8*k+5)-1/(8*k+6))/16**k, [0,inf])
2/nsum(lambda k: (-1)**k*(4*k+1)*(fac2(2*k-1)/fac2(2*k))**3, [0,inf])
nsum(lambda k: 72/(k*expm1(k*pi))-96/(k*expm1(2*pi*k))+24/(k*expm1(4*pi*k)), [1,inf])
1/nsum(lambda k: binomial(2*k,k)**3*(42*k+5)/2**(12*k+4), [0,inf])
4/nsum(lambda k: (-1)**k*(1123+21460*k)*fac2(2*k-1)*fac2(4*k-1)/(882**(2*k+1)*32**k*fac(k)**3), [0,inf])
9801/sqrt(8)/nsum(lambda k: fac(4*k)*(1103+26390*k)/(fac(k)**4*396**(4*k)), [0,inf])
426880*sqrt(10005)/nsum(lambda k: (-1)**k*fac(6*k)*(13591409+545140134*k)/(fac(k)**3*fac(3*k)*(640320**3)**k), [0,inf])
4/nsum(lambda k: (6*k+1)*rf(0.5,k)**3/(4**k*fac(k)**3), [0,inf])
(ln(8)+sqrt(48*nsum(lambda m,n: (-1)**(m+n)/(m**2+n**2), [1,inf],[1,inf]) + 9*log(2)**2))/2
-nsum(lambda x,y: (-1)**(x+y)/(x**2+y**2), [-inf,inf], [-inf,inf], ignore=True)/ln2
2*nsum(lambda k: sin(k)/k, [1,inf])+1
quad(lambda x: 2/(x**2+1), [0,inf])
quad(lambda x: exp(-x**2), [-inf,inf])**2
2*quad(lambda x: sqrt(1-x**2), [-1,1])
chop(quad(lambda z: 1/(2j*z), [1,j,-1,-j,1]))
3*(4*log(2+sqrt(3))-quad(lambda x,y: 1/sqrt(1+x**2+y**2), [-1,1],[-1,1]))/2
sqrt(8*quad(lambda x,y: 1/(1-(x*y)**2), [0,1],[0,1]))
sqrt(6*quad(lambda x,y: 1/(1-x*y), [0,1],[0,1]))
sqrt(6*quad(lambda x: x/expm1(x), [0,inf]))
quad(lambda x: (16*x-16)/(x**4-2*x**3+4*x-4), [0,1])
quad(lambda x: sqrt(x-x**2), [0,0.25])*24+3*sqrt(3)/4
mpf(22)/7 - quad(lambda x: x**4*(1-x)**4/(1+x**2), [0,1])
mpf(355)/113 - quad(lambda x: x**8*(1-x)**8*(25+816*x**2)/(1+x**2), [0,1])/3164
2*quadosc(lambda x: sin(x)/x, [0,inf], omega=1)
40*quadosc(lambda x: sin(x)**6/x**6, [0,inf], omega=1)/11
e*quadosc(lambda x: cos(x)/(1+x**2), [-inf,inf], omega=1)
8*quadosc(lambda x: cos(x**2), [0,inf], zeros=lambda n: sqrt(n))**2
2*quadosc(lambda x: sin(exp(x)), [1,inf], zeros=ln)+2*si(e)
exp(2*quad(loggamma, [0,1]))/2
2*nprod(lambda k: sec(pi/2**k), [2,inf])
s=lambda k: sqrt(0.5+s(k-1)/2) if k else 0; 2/nprod(s, [1,inf])
s=lambda k: sqrt(2+s(k-1)) if k else 0; limit(lambda k: sqrt(2-s(k))*2**(k+1), inf)
2*nprod(lambda k: (2*k)**2/((2*k-1)*(2*k+1)), [1,inf])
2*nprod(lambda k: (4*k**2)/(4*k**2-1), [1, inf])
sqrt(6*ln(nprod(lambda k: exp(1/k**2), [1,inf])))
nprod(lambda k: (k**2-1)/(k**2+1), [2,inf])/csch(pi)
nprod(lambda k: (k**2-1)/(k**2+1), [2,inf])*sinh(pi)
nprod(lambda k: (k**4-1)/(k**4+1), [2, inf])*(cosh(sqrt(2)*pi)-cos(sqrt(2)*pi))/sinh(pi)
sinh(pi)/nprod(lambda k: (1-1/k**4), [2, inf])/4
sinh(pi)/nprod(lambda k: (1+1/k**2), [2, inf])/2
(exp(1+euler/2)/nprod(lambda n: (1+1/n)**n * exp(1/(2*n)-1), [1, inf]))**2/2
3*sqrt(2)*cosh(pi*sqrt(3)/2)**2*csch(pi*sqrt(2))/nprod(lambda k: (1+1/k+1/k**2)**2/(1+2/k+3/k**2), [1, inf])
2/e*nprod(lambda k: (1+2/k)**((-1)**(k+1)*k), [1,inf])
limit(lambda k: 16**k/(k*binomial(2*k,k)**2), inf)
limit(lambda x: 4*x*hyp1f2(0.5,1.5,1.5,-x**2), inf)
1/log(limit(lambda n: nprod(lambda k: pi/(2*atan(k)), [n,2*n]), inf),4)
limit(lambda k: 2**(4*k+1)*fac(k)**4/(2*k+1)/fac(2*k)**2, inf)
limit(lambda k: fac(k) / (sqrt(k)*(k/e)**k), inf)**2/2
limit(lambda k: (-(-1)**k*bernoulli(2*k)*2**(2*k-1)/fac(2*k))**(-1/(2*k)), inf)
limit(lambda k: besseljzero(1,k)/k, inf)
1/limit(lambda x: airyai(x)*2*x**0.25*exp(2*x**1.5/3), inf, exp=True)**2
1/limit(lambda x: airybi(x)*x**0.25*exp(-2*x**1.5/3), inf, exp=True)**2

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