Message 337658 - Python tracker (original) (raw)

I've done some spot checks of NormDist.pdf and .cdf and compared the results to those returned by my TI Nspire calculator.

So far, the PDF has matched that of the Nspire to 12 decimal places (the limit the calculator will show), but the CDF differs on or about the 8th decimal place:

py> x = statistics.NormalDist(2, 1.3) py> x.cdf(5.374) 0.9952757439207682

Nspire normCdf(-∞, 5.372, 2, 1.3) returns 0.995275710979

difference of 3.294176820212158e-08

py> x.cdf(-0.23) 0.04313736707891003

Nspire normCdf(-∞, -0.23, 2, 1.3) returns 0.043137332077

difference of 3.500191003008579e-08

Wolfram Alpha doesn't help me decide which is correct, as it doesn't show enough decimal places.

https://www.wolframalpha.com/input/?i=CDF[+NormalDistribution[2,+1.3],+5.374+]

https://www.wolframalpha.com/input/?i=CDF[+NormalDistribution[2,+1.3],+-0.23+]

Do we care about this difference? Should I raise a new ticket for it?