# [R] missing value where TRUE/FALSE needed ERROR

Maram SAlem marammagdysalem at gmail.com
Tue Feb 9 16:03:24 CET 2016

```Thanks for helping thanoon.
I used the if()  {
....
} else {
.....
}
and it worked better

On 9 February 2016 at 15:56, thanoon younis <thanoon.younis80 at gmail.com>
wrote:

> Hi,
>
> Try to check the function only
> if (runif(1) <= accept.prob) beta.cand else beta.curr
> something is missing here. Why you take only runif(1).
>
> Regards
>
> On 9 February 2016 at 16:01, Maram SAlem <marammagdysalem at gmail.com>
> wrote:
>
>> Hi all,
>>
>> I'm trying to write a function to implement a Metropolis-within-Gibbs
>> algorithm for two parameters.I'm including a naive version here so as to
>> be
>> able to spot the error I got. So I first generate the vectors, X and R,
>> that will help to start the algorithm using (for example):
>>
>> n=8; m=5; p=0.1; t=0.9 ; JH=10;
>>
>> R <- numeric(m)
>>
>> W <- numeric(m)
>>
>> V <- numeric(m)
>>
>> U <- numeric(m)
>>
>> X <- numeric(m)
>>
>> Bay.alpha<- numeric (JH)
>>
>> Bay.beta<- numeric (JH)
>>
>> Bay.Surv <- numeric (JH)
>>
>> hyp=c(3,15,6,22.5)
>>
>> theta<-c(0.2,2)
>>
>>
>> alpha.curr<-theta
>>
>> beta.curr<- theta
>>
>>
>>
>> R<-rbinom(1, n-m, p)
>>
>>  for (i in 2:m-1) {
>>
>>  R[i]<-rbinom(1,n-m-sum(R[1:i-1]),p)
>>
>>  }
>>
>>  R[m]<-n-m-sum(R[1:m-1])
>>
>> W<-runif(m, min = 0, max = 1)
>>
>> for (i in 1:m){
>>
>>  V[i]<-W[i]^(1/(i+sum(R[(m-i+1):m])))
>>
>> }
>>
>> for (i in 1:m){
>>
>>  U[i]<- 1- prod(V[(m-i+1):m])
>>
>> }
>>
>> for (i in 1:m){
>>
>> X[i]<- ((-1/theta)*log(1-U[i]))^(1/theta)
>>
>> }
>>
>>
>> Then, I defined three functions 1- alpha.update() for updating alpha
>> (Gibbs
>> step) 2- bettarg(), for the target distribution of beta 3- beta.update()
>> for updating beta using a Metropolis Hastings technique.
>>
>>
>>    alpha.update=function(X, R, alpha.curr, beta.curr ,m, hyp)
>>
>>   {
>>
>>   o<-numeric(m)
>>
>>      for (i in 1:m) {
>>
>>        o[i]<- (1+R[i])*((X[i])^(beta.curr))
>>
>>         }
>>
>>    sh<-sum(o) + hyp + (hyp* beta.curr)
>>
>>    rg<-rgamma(1, shape= m+hyp+hyp , rate = sh )
>>
>>    return(rg)
>>
>>    }
>>
>>
>>
>>    bettarg<- function(X, R, alpha.curr, beta.curr ,m, hyp)
>>
>>        {
>>
>>            o<-numeric(m)
>>
>>            for (i in 1:m) {
>>
>>        o[i]<- (1+R[i])*((X[i])^( beta.curr))
>>
>>         }
>>
>>       bt<- beta.curr ^(m+hyp-1) * prod((X)^( beta.curr -1)) *
>> exp(-1*alpha.curr *(sum(o) +      (hyp* beta.curr)))
>>
>>     return(bt)
>>
>>        }
>>
>>        beta.update<- function (X, R, alpha.curr, beta.curr ,m, hyp,
>> cand.sd)
>>
>>        {
>>
>>        beta.cand<- rnorm(1, mean = beta.curr, sd = cand.sd)
>>
>>       AB<- bettarg (X, R, alpha.curr, beta.curr = beta.cand ,m, hyp)
>>
>>       CD<- bettarg (X, R, alpha.curr, beta.curr ,m, hyp)
>>
>>       accept.prob <- AB/CD
>>
>>      if (runif(1) <= accept.prob)
>>
>>      beta.cand
>>
>>     else  beta.curr
>>
>>      }
>>
>>
>> Then I started a tiny chain using ten iterations but got this ERROR:
>>
>>
>> for (k in 1:JH)
>>
>> {
>>
>> alpha.curr<- alpha.update(X, R, alpha.curr, beta.curr ,m, hyp)
>>
>>  Bay.alpha[k]<-alpha.curr
>>
>> beta.curr<- beta.update (X, R, alpha.curr, beta.curr ,m, hyp, cand.sd=2)
>>
>>      Bay.beta[k]<- beta.curr
>>
>>      Bay.Surv [k]<- exp (-1*Bay.alpha[k] * (t)^Bay.beta[k])
>>
>>      }
>>
>>
>> Error in if (runif(1) <= accept.prob) beta.cand else beta.curr :
>>
>>   missing value where TRUE/FALSE needed
>>
>>
>> In rgamma(1, shape = m + hyp + hyp, rate = sh) : NAs produced
>>
>>
>> I ran the code several times for only one iteration but everything was
>> fine
>> with no errors or warnings, so I don't know from where does the missing
>> value/ NA come from?
>>
>> In addition, I want to calculate the acceptance rate for the
>> Metropolis-Hastings step, is this possible?
>>
>> Any help would be appreciated.
>> Thanks,
>>
>> Maram Salem
>>
>>         [[alternative HTML version deleted]]
>>
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>> and provide commented, minimal, self-contained, reproducible code.
>>
>
>
>
> --
> Thanoon Y. Thanoon
> PhD Candidate
> Department of Mathematical Sciences
> Faculty of Science
> University Technology Malaysia, UTM
> E.Mail: Thanoon.younis80 at gmail.com
> E.Mail: dawn_prayer80 at yahoo.com