Re: [R] help for the first poster- a simple question

From: Xuejun Qin <xjq_at_chg.duhs.duke.edu>
Date: Mon, 03 Mar 2008 14:12:34 -0500

Thanks for all response. Here is more closer to my question, p<-0.05

f<-0.05

ld<-sqrt(f* (1 - f) * p * (1 - p))

D <- (p * (1 - f) - ld)/p

d <- ((1 - p) * f - ld)/(1 - p)

haplo<-data.frame(D,d)

> haplo

              D d
1 -1.387779e-16 -7.304099e-18

cond1<-pmin(haplo[,1],haplo[,2])

haplo[cond1>=0,]

But the program cannot get right one, because

 -1.387779e-16>=0 is FALSE

 -7.304099e-18>=0 is FALSE

Thank you!

xj.

> On Mon, 2008-03-03 at 12:52 -0500, Xuejun Qin wrote:
>> Hi, there,
>> I cannot get accurate value for calculation.
>> for example:
>> ld<-
>> 0.05*0.95-ld=-6.938894e-18
>> 0.05*0.95-ld==0 is False.
>>
>> I met this problem in my program, how can I handle it. Thanks.
>
> Answer 1:
>
> Read FAQ 7.31 -
>
> http://cran.r-project.org/doc/FAQ/R-FAQ.html#Why-doesn_0027t-R-think-these-numbers-are-equal_003f
>
> Answer 2:
>
> Use all.equal()
>
>> ld<-sqrt(1*0.05*0.95*0.05*0.95)
>> 0.05*0.95-ld
> [1] -6.938894e-18
>> 0.05*0.95-ld==0
> [1] FALSE
>> all.equal(0.05*0.95-ld, 0)
> [1] TRUE
>
>>
>>
>> xj.
>
> HTH
>
> G
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> Dr. Gavin Simpson [t] +44 (0)20 7679 0522
> ECRC, UCL Geography, [f] +44 (0)20 7679 0565
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