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Compute the quantile function for the normal distribution. - like Excel NORMINV
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/// Original C++ implementation found at http://www.wilmott.com/messageview.cfm?catid=10&threadid=38771 | |
/// C# implementation found at http://weblogs.asp.net/esanchez/archive/2010/07/29/a-quick-and-dirty-implementation-of-excel-norminv-function-in-c.aspx | |
/* | |
* Compute the quantile function for the normal distribution. | |
* | |
* For small to moderate probabilities, algorithm referenced | |
* below is used to obtain an initial approximation which is | |
* polished with a final Newton step. | |
* | |
* For very large arguments, an algorithm of Wichura is used. | |
* | |
* REFERENCE | |
* | |
* Beasley, J. D. and S. G. Springer (1977). | |
* Algorithm AS 111: The percentage points of the normal distribution, | |
* Applied Statistics, 26, 118-121. | |
* | |
* Wichura, M.J. (1988). | |
* Algorithm AS 241: The Percentage Points of the Normal Distribution. | |
* Applied Statistics, 37, 477-484. | |
*/ | |
function normsInv(p, mu, sigma) | |
{ | |
if (p < 0 || p > 1) | |
{ | |
throw "The probality p must be bigger than 0 and smaller than 1"; | |
} | |
if (sigma < 0) | |
{ | |
throw "The standard deviation sigma must be positive"; | |
} | |
if (p == 0) | |
{ | |
return -Infinity; | |
} | |
if (p == 1) | |
{ | |
return Infinity; | |
} | |
if (sigma == 0) | |
{ | |
return mu; | |
} | |
var q, r, val; | |
q = p - 0.5; | |
/*-- use AS 241 --- */ | |
/* double ppnd16_(double *p, long *ifault)*/ | |
/* ALGORITHM AS241 APPL. STATIST. (1988) VOL. 37, NO. 3 | |
Produces the normal deviate Z corresponding to a given lower | |
tail area of P; Z is accurate to about 1 part in 10**16. | |
*/ | |
if (Math.abs(q) <= .425) | |
{/* 0.075 <= p <= 0.925 */ | |
r = .180625 - q * q; | |
val = | |
q * (((((((r * 2509.0809287301226727 + | |
33430.575583588128105) * r + 67265.770927008700853) * r + | |
45921.953931549871457) * r + 13731.693765509461125) * r + | |
1971.5909503065514427) * r + 133.14166789178437745) * r + | |
3.387132872796366608) | |
/ (((((((r * 5226.495278852854561 + | |
28729.085735721942674) * r + 39307.89580009271061) * r + | |
21213.794301586595867) * r + 5394.1960214247511077) * r + | |
687.1870074920579083) * r + 42.313330701600911252) * r + 1); | |
} | |
else | |
{ /* closer than 0.075 from {0,1} boundary */ | |
/* r = min(p, 1-p) < 0.075 */ | |
if (q > 0) | |
r = 1 - p; | |
else | |
r = p; | |
r = Math.sqrt(-Math.log(r)); | |
/* r = sqrt(-log(r)) <==> min(p, 1-p) = exp( - r^2 ) */ | |
if (r <= 5) | |
{ /* <==> min(p,1-p) >= exp(-25) ~= 1.3888e-11 */ | |
r += -1.6; | |
val = (((((((r * 7.7454501427834140764e-4 + | |
.0227238449892691845833) * r + .24178072517745061177) * | |
r + 1.27045825245236838258) * r + | |
3.64784832476320460504) * r + 5.7694972214606914055) * | |
r + 4.6303378461565452959) * r + | |
1.42343711074968357734) | |
/ (((((((r * | |
1.05075007164441684324e-9 + 5.475938084995344946e-4) * | |
r + .0151986665636164571966) * r + | |
.14810397642748007459) * r + .68976733498510000455) * | |
r + 1.6763848301838038494) * r + | |
2.05319162663775882187) * r + 1); | |
} | |
else | |
{ /* very close to 0 or 1 */ | |
r += -5; | |
val = (((((((r * 2.01033439929228813265e-7 + | |
2.71155556874348757815e-5) * r + | |
.0012426609473880784386) * r + .026532189526576123093) * | |
r + .29656057182850489123) * r + | |
1.7848265399172913358) * r + 5.4637849111641143699) * | |
r + 6.6579046435011037772) | |
/ (((((((r * | |
2.04426310338993978564e-15 + 1.4215117583164458887e-7) * | |
r + 1.8463183175100546818e-5) * r + | |
7.868691311456132591e-4) * r + .0148753612908506148525) | |
* r + .13692988092273580531) * r + | |
.59983220655588793769) * r + 1); | |
} | |
if (q < 0.0) | |
{ | |
val = -val; | |
} | |
} | |
return mu + sigma * val; | |
} | |
// normInv(0.2, 3.5, 0.707106781); |
Thanks for your work!
There's a typing error in this example that prevents it from running. Row 81: replace Math.Sqrt with Math.sqrt
// normInv(0.2, 3.5, 0,707106781);
A minor thing: the last number has a comma while it should be a dot?
It's Math.sqrt
not Math.Sqrt
. Thank you for the snippet.
thank you very much, did you know for gumbelinv(), loginv(), logpersoninv() && normaldist(), gumbeldist(), logdist(), logpersondist() ?
I waiting your answer :)
@dginanjar13, I've used some of them but not in JavaScript and have no use for them.
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Thank you very much! Add another language to it (java): http://info.michael-simons.eu/2013/02/21/java-implementation-of-excels-statistical-functions-norminv/