[R] Is it a bug ?

[Uwe Ligges]

I don't get your point, because

 > exp(-(-3)^2.2)
[1] NaN

is correct. A negative value to the power of a non-integer is undefined 
in IR. Of course it is defined as a complex number:

 > exp(-(-3+0i)^2.2)
[1] 1.096538e-04-3.47404e-05i

Uwe Ligges




Giuseppe PEDRAZZI wrote:
> 		[[diverted from R-bugs to R-help by the list maintainer]]
> 
> Dear Friend and distinguished R gurus,
> 
> first of all really thank you very much for the marvellous tool that is R.
> 
> I am using R 2.5.0,  windows XP - italian language.
> 
> I was perfoming some calculation on fractional exponential and
> I found a strange behaviour. I do not know if it is really a bug, but I would expect
> a different answer from R.
> 
> I was trying the following :
> 
> x <- seq(-3,3, by =0.1)
> n <- 2.2
> y <- exp(-x^n)
> 
> well, the y vector contains (NaN for all negative value of x)
> 
> but if you ask for single value calculation like
> 
> y <- exp(-(-3)^2.2) or 
> 
> y <- exp(-(-2.9)^2.2)
> 
> the answer is correct. 
> It seem it does not make the calculation in vector form.
> 
> I got the same behaviour (NaN)  in a for loop
> 
>> for(i in 1:length(x)) y[i]=exp(x[i]^n)
>> y
>  [1]           NaN          NaN          NaN          NaN          NaN          NaN          NaN          NaN          NaN
> [10]          NaN          NaN          NaN          NaN          NaN          NaN          NaN          NaN          NaN
> [19]          NaN          NaN          NaN          NaN          NaN          NaN          NaN          NaN          NaN
> [28]          NaN          NaN          NaN     1.000000     1.006330     1.029416     1.073302     1.142488     1.243137
> [37]     1.384082     1.578166     1.844237     2.210260     2.718282     3.432491     4.452553     5.936068     8.137120
> [46]    11.473746    16.648415    24.867680    38.251295    60.611092    98.967689   166.572985   289.077778   517.425935
> [55]   955.487320  1820.793570  3581.521323  7273.674928 15255.446778 33050.861013 73982.100407
> 
> Is it strange or did I miss something ?
> 
> Many thanks for the attention.
> 
> 
> Very best regards
> 
> Giuseppe Pedrazzi
> Dept Public Health, Physics Division
> University of Parma, Italy
> 	[[alternative HTML version deleted]]
> 
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