From Martin Maechler <maechler@stat.math.ethz.ch>  Tue Apr 15 22:52:01 1997
From: Martin Maechler <maechler@stat.math.ethz.ch> (Martin Maechler)
Date: Tue, 15 Apr 97 23:52:01 +0200
Subject: R-alpha: Bug & Patch  in  dbeta.c  (0.50 - PreR 7)
In-Reply-To: <Pine.SUN.3.95.970415125913.21998B-100000@uhura> (message from
 Thomas Lumley on Tue, 15 Apr 1997 13:02:55 -0700 (PDT))
Message-ID: <9704152152.AA01582@>

Of course ! (--- silly me)

S-plus actually always returns 0 here;  but your solution is mathematically
correct where S is NOT!

The "bad" thing about R is only that we still don't have IEEE arithmetic.
Will get 'NA' instead of 'Inf'  ...


Thomas Lumley :
>> On Tue, 15 Apr 1997, Martin Maechler wrote:
>> 
>> > dbeta(1, a,b)  would return 1 instead of 0.
>> 
>> Shouldn't it be 1 for b=1, Inf for b<1 and 0 for b>1 at x=1 (and similar
>> behaviour at x=0)?
>> 
>> ie 
>> double dbeta(double x, double a, double b)
>> {
>>         if (a <= 0.0 || b <= 0.0)
>>                 DOMAIN_ERROR;
>>         if (x < 0)
>>                 return 0.0;
>>         if (x > 1.0)
>>                 return 0.0;
>>         return MATH_CHECK(pow(x, a - 1) * pow(1.0 - x, b - 1.0) / beta(a,
>> b));
>> }
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R-alpha: Bug & Patch in dbeta.c (0.50 - PreR 7)
Martin Maechler