Thursday, November 25, 2021

HP 17BII+: Update to Normal CDF Formula - Don Phillips

 HP 17BII+:  Update to Normal CDF Formula - Don Phillips


On March 31, 2019, I posted a formula calculate the normal cumulative distributive function (normal CDF) for x ≥ 0:


http://edspi31415.blogspot.com/2019/03/hp-17bii-normal-distribution-and-random.html


Don Phillips provided us with an updated formula to include negative values of x.   Much gratitude for allowing me to post this formula:


NCDF=L(ANS:1-EXP(-ABS(X)^2÷2)÷SQRT(2×PI)×(.4361836×L(T:INV(1+.33267×ABS(X)))-.1201676×G(T)^2+.9372980×G(T)^3))×0+IF(X<0:1-G(ANS):G(ANS))


Example Calculations:

X = -2.50,  NCDF = 0.00622

X = -1.50, NCDF = 0.06680

X = -0.50, NCDF = 0.30855

X = 0.00, NCDF = 0.50000

X = 0.50, NCDF = 0.69145

X = 1.00, NCDF = 0.84135

X = 2.00, NCDF = 0.97724


Thank you Don, Eddie. 

All original content copyright, © 2011-2021.  Edward Shore.   Unauthorized use and/or unauthorized distribution for commercial purposes without express and written permission from the author is strictly prohibited.  This blog entry may be distributed for noncommercial purposes, provided that full credit is given to the author. 


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