[R] bug or bizarre feature?

[David Winsemius]

Proably ole Faq 7.21 again. You are using floating point numbers and  
expecting coercion to result in upward rounding.

My guess is that if you use trunc(udim) you will get a different number.

Yep:
 > trunc(udim)
[1] 115



On Nov 30, 2009, at 2:15 PM, Rupert Mazzucco wrote:

> Hello,
>
> I'm running into a very strange problem:
>
>> xrange <- c(-2.5,2.5)
>> xdim <- 100
>> mobility <- 0.1
>> slope <- 1.16
>> urange <- slope*xrange
>>        udim <- max(slope*xdim,5)
>>        du <- (urange[2]-urange[1])/udim
>>        uvec <- urange[1]+(1:udim-0.5)*du
>>        # type dependent weight function
>>        ckern <- array(0,dim=c(udim,udim))
>>        diag(ckern) = wfun(uvec,slope,mobility)
> Error in `diag<-`(`*tmp*`, value = c(0.992300064325398,  
> 0.990746129315703,  :
>  replacement diagonal has wrong length
>
> It turns out that the array ckern has the wrong size for some reason.
> Instead of 116x116, it is only 115x115.
>
>> udim
> [1] 116
>> length(uvec)
> [1] 116
>> length(wfun(uvec,slope,mobility))
> [1] 116
>> dim(ckern)
> [1] 115 115
>
> The "taint" or whatever that is, is even transferable
>
>> n <- udim
>> n
> [1] 116
>> ckern <- array(0,dim=c(n,n))
>> dim(ckern)
> [1] 115 115
>> m <- n
>> m
> [1] 116
>> ckern <- array(0,dim=c(m,m))
>> dim(ckern)
> [1] 115 115
>
> But when I set it explicitly, it does what it should:
>
>> n <- 116
>> n
> [1] 116
>> ckern <- array(0,dim=c(n,n))
>> dim(ckern)
> [1] 116 116
>
> Note that the funny behavior seems to be peculiar to this one value  
> of slope <- 1.16,
> many others work fine, e.g.
>
>> slope <- 1.08
>> urange <- slope*xrange
>>        udim <- max(slope*xdim,5)
>>        du <- (urange[2]-urange[1])/udim
>>        uvec <- urange[1]+(1:udim-0.5)*du
>>        # type dependent weight function
>>        ckern <- array(0,dim=c(udim,udim))
>>        diag(ckern) = wfun(uvec,slope,mobility)
>> dim(ckern)
> [1] 108 108
>
> This is R 2.10.0, but also happened in 2.8.0. Can anybody tell me what
> is going on here, and how I can get my array to be the right size?
>
> Thanks,
> Rupert
>
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David Winsemius, MD
Heritage Laboratories
West Hartford, CT