Talk:Welch's t-test: Difference between revisions
→Implementing Algorithm... existing libraries don't calculate correct numbers
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:There is another problem: you damaged the original function, by replacing <code>*ifault = 0;</code> with <code>ifault = 0;</code>, replacing ifault with a null pointer. This will crash the program with a null pointer dereference whenever the arguments passed to betain are incorrect (hence ifault is assigned a value). I didn't check if you introduced another problem in the code.
:Your statement that ''existing libraries don't calculate correct numbers'' is wrong.
:[[User:Eoraptor|Eoraptor]] ([[User talk:Eoraptor|talk]]) 19:31, 28 December 2017 (UTC)
::For the record, here is a quick Stata translation of this betain implementation.
::<lang stata>mata
function betain(x,p,q,beta) {
acu = 1e-15
value = x
/* Check the input arguments. */
if (p<=0 | q<=0 | x<0 | x>1) return(.)
/* Special cases. */
if (x==0 | x==1) {
return(value)
}
/* Change tail if necessary and determine S. */
psq = p+q
if (p<psq*x) {
xx = 1-x
cx = x
pp = q
qq = p
indx = 1
}
else {
xx = x
cx = 1-x
pp = p
qq = q
indx = 0
}
term = ai = value = 1
ns = floor(qq+cx*psq)
/* Use the Soper reduction formula. */
rx = xx/cx
temp = qq-ai
if (ns==0) rx = xx
while(1) {
term = term*temp*rx/(pp+ai)
value = value+term
temp = abs(term)
if (temp<=acu & temp<=acu*value) {
value = value*exp(pp*log(xx)+(qq-1)*log(cx)-beta)/pp
return(indx?1-value:value)
}
ai++
if (--ns>=0) {
temp = qq-ai
if (ns==0) rx=xx
}
else {
temp = psq++
}
}
}
end</lang>
::[[User:Eoraptor|Eoraptor]] ([[User talk:Eoraptor|talk]]) 21:31, 28 December 2017 (UTC)
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