[R] Problem in log

[Sarah Goslee]

> Here p[i] <- 1 - exp(-alpha*d^(-beta))> so,  log(p[i]) produces NaNs when exp(-alpha*d^(-beta)) is greater than 1.> How can I remove it.After generating the out put we can omit it, but the> problem is different.

Wait... you're complaining that you can't take the natural log of a negative
number in R?

You can't do that anywhere. What do you expect to happen? The log of a
negative number IS NaN.

Sarah
On Tue, Nov 29, 2011 at 6:28 PM, Gyanendra Pokharel
<gyanendra.pokharel at gmail.com> wrote:
> I have following code:
> loglikelihood <- function(alpha,beta= 0.1){
>    loglh<-0
>    d<-0
>    p<-0
>    k<-NULL
>    data<-read.table("epidemic.txt",header = TRUE)
>    attach(data, warn.conflicts = F)
>    k <-which(inftime==1)
>    d <- (sqrt((x-x[k])^2+(y-y[k])^2))^(-beta)
>    p<-1 - exp(-alpha*d)
>    for(i in 1:100){
>        if(i!=k){
>            if(inftime[i]==0){
>                loglh<-loglh +log(1-p[i])
>            }
>            if(inftime[i]==2){
>                loglh<-loglh + log(p[i])
>            }
>        }
>    }
>    return(loglh)
> }
> Here p[i] <- 1 - exp(-alpha*d^(-beta))
> so,  log(p[i]) produces NaNs when exp(-alpha*d^(-beta)) is greater than 1.
> How can I remove it.After generating the out put we can omit it, but the
> problem is different.
>
> On Tue, Nov 29, 2011 at 5:22 PM, Gyanendra Pokharel <
> gyanendra.pokharel at gmail.com> wrote:
>
>> No, that,s not a problem Michael,
>> I have following code:
>> loglikelihood <- function(alpha,beta= 0.1){
>>     loglh<-0
>>     d<-0
>>     p<-0
>>     k<-NULL
>>     data<-read.table("epidemic.txt",header = TRUE)
>>     attach(data, warn.conflicts = F)
>>     k <-which(inftime==1)
>>     d <- (sqrt((x-x[k])^2+(y-y[k])^2))^(-beta)
>>     p<-1 - exp(-alpha*d)
>>     for(i in 1:100){
>>         if(i!=k){
>>             if(inftime[i]==0){
>>                 loglh<-loglh +log(1-p[i])
>>             }
>>             if(inftime[i]==2){
>>                 loglh<-loglh + log(p[i])
>>             }
>>         }
>>     }
>>     return(loglh)
>> }
>> Here p[i] <- 1 - exp(-alpha*d^(-beta))
>> so,  log(p[i]) produces NaNs when exp(-alpha*d^(-beta)) is greater than 1.
>> How can I remove it.After generating the out put we can omit it, but the
>> problem is different.
>>
>>

-- 
Sarah Goslee
http://www.functionaldiversity.org