[Q & A]Defining a stepwise uniform distribution using WinBUGS?

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I want to define a distribution in my model of the form: P(x=10)=0.10, P(x=15)=0.20, P(x=20)=0.70

The WinBUGS FAQ says it is possible construct my own discrete uniform distribution as a categorical variable with a uniform prior and which can take on the necessary integer values. See the blockerht example in the first part of the manual.

I looked the example up, I think it is this one: "A hierarchical t-distribution with unknown degrees of freedom"

At the model specification they do something like:

1. for (n in 1:Nbins) {
   
2.    prior[n] <- 1/Nbins;   # Uniform prior on v
   
3. }
   
4. k ~ dcat(prior[]);

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Which does define a discrete uniform. But I don't know how to get to the form I need. Can anyone help me?

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关键词：distribution defining stepwise Uniform winbugs necessary something possible example values

If I understand your question correctly, you do not need the loop...

1. #BUGS script to obtain distribution
   
2. m1<-"model{
   
3.   ind ~ dcat(p[])
   
4.   pmix <- x[ind]
   
5. }"
   
6. writeLines(m1,"m1.txt")
   
7. 
   
8. #simulate from the distribution   
   
9. library("R2OpenBUGS")
   
10. m1.bug<-bugs(data = list(x=c(10, 15, 20), p=c(0.1,0.2,0.7)),
    
11.              inits = NULL,
    
12.              param = "pmix",
    
13.              model = "m1.txt",
    
14.              n.iter = 1100, n.burnin = 100, n.chains = 1, n.thin=1, DIC=FALSE)
    
15. 
    
16. hist(m1.bug$sims.list$pmix)

复制代码

should work...

I am learning how to do this myself. I wonder if you can do this:

prior[10] <- .1
prior[15] <- .2
prior[20] <- .7
x ~ dcat(prior[])