[R] Is it a bug ?
Thomas Lumley
tlumley at u.washington.edu
Thu Jul 5 16:48:39 CEST 2007
On Thu, 5 Jul 2007, Giuseppe PEDRAZZI wrote:
> 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)
Yes. Non-integer powers of negative numbers are undefined (unless you use
complex numbers).
> 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.
I get NaN for both of these. Perhaps you mean exp(-2.9^2.2)? This gives
a valid answer, but that is because it is exp(-(2.9^2.2)) not
exp((-2.9)^2.2)
> 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 ?
You missed something. It is not clear what you missed because some of your
examples do not give the answer you say they give.
-thomas
More information about the R-help
mailing list