Probability Functions: order of arguments insanity
09-12-2014, 04:55 AM
Post: #1
 rkf Member Posts: 65 Joined: Apr 2014
Probability Functions: order of arguments insanity
A student in a German HP Prime forum came up with the reasonable question, why following inconsistency was implemented (cited via copy&paste from User_Guide_EN.pdf):

for the density function:

BINOMIAL(n,k,p)

for the cumulative distribution function:

BINOMIAL_CDF(n,p,k)

What the heck was the reason for swapping the order of 2nd and 3rd arguments? Please please HP, enlighten us!!

Kind regards,
Ralf.
09-13-2014, 08:31 AM
Post: #2
 parisse Senior Member Posts: 1,112 Joined: Dec 2013
RE: Probability Functions: order of arguments insanity
The CAS accepts both syntax for binomial: binomial(n,p,k) and binomial(n,k,p), it checks whether the second argument is a real in 0..1 or an integer. The reason to accept both syntax is for compatibility with binomial(n,k)==comb(n,k) and binomial_cdf and icdf argument order consistency.
09-21-2014, 05:14 PM (This post was last modified: 09-21-2014 05:18 PM by Primeoprime.)
Post: #3
 Primeoprime Junior Member Posts: 1 Joined: Sep 2014
RE: Probability Functions: order of arguments insanity
(09-13-2014 08:31 AM)parisse Wrote:  The CAS accepts both syntax for binomial: binomial(n,p,k) and binomial(n,k,p),

Hallo Parisse,

mine doesn´t accept both.. it gives me error in that case:binomial(n,p,k) and also in that case: binominal_CDF(n,k,p) Shows "Fehler:ungültige Eingabe" (it knows German)

My Casio fx-cp 400 CAS, my Ti-nspire Cx CAS and my Casio fx-CG20 too accept in each case only one syntax (defenitely!) , but the same for binomial and binominal_CDF.

So I need no brain capacity to pay attention what biominal entry is asked and it´s so much easier for me to do math at school.

I guess Hp prime is not build for pupils and students. And I can`t recommened HP prime to other pupils in my school. Better they use Casio fx-cp 400 or Ti-nspire Cx CAS or Casio fx-CG20 , which are easier to understand by intuition.

Best regards!
und herzlichst!
Naomi

" All those who agree with me and believe in telekinetics raise my right arm now !"
09-21-2014, 09:23 PM
Post: #4
 Michael Junior Member Posts: 41 Joined: Dec 2013
RE: Probability Functions: order of arguments insanity
Keep on rocking, Naomi!
09-23-2014, 06:45 AM
Post: #5
 parisse Senior Member Posts: 1,112 Joined: Dec 2013
RE: Probability Functions: order of arguments insanity
(09-21-2014 05:14 PM)Primeoprime Wrote:
(09-13-2014 08:31 AM)parisse Wrote:  The CAS accepts both syntax for binomial: binomial(n,p,k) and binomial(n,k,p),

Hallo Parisse,

mine doesn´t accept both.. it gives me error in that case:binomial(n,p,k) and also in that case: binominal_CDF(n,k,p) Shows "Fehler:ungültige Eingabe" (it knows German)
Make sure you enter the commandnames in lowercase. Also note that binomial_cdf and binomial_icdf take p as second argument, since binomial_[i]cdf(n,k) does not mean anything.
09-24-2014, 05:52 AM
Post: #6
 rkf Member Posts: 65 Joined: Apr 2014
RE: Probability Functions: order of arguments insanity
(09-13-2014 08:31 AM)parisse Wrote:  The CAS accepts both syntax for binomial: binomial(n,p,k) and binomial(n,k,p), it checks whether the second argument is a real in 0..1 or an integer. ...

I suggest a look at this topic in a German discussion forum, where basically is shown my means of examples, that the statement above is true only in some special cases, but not in general.
09-24-2014, 07:21 AM
Post: #7
 parisse Senior Member Posts: 1,112 Joined: Dec 2013
RE: Probability Functions: order of arguments insanity
It's of course true if p and k have values, not if they are symbolic. There is no good solution anyway, since users will expect p as an optionnal 3rd argument to binomial(n,k) and will expect argument order consistency with binomial_cdf/icdf, whatever it means since the third arg has nothing to do with the k of binomial(n,k,p), you should see this k as a disappearing argument.
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