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rdistributionbeta

Why does using dtrunc give me error message?

I want to truncate beta distribution that is the value of the beta distribution in [0,0.2] is zero. I used "dtrunc" as follows:

I encountered the following error message:

"Error in g(x, ...) : argument "shape1" is missing, with no default"

Could yo please let me know what is happening?

p <-seq(0,1,length=1000)
pdf <- dtrunc(p, spec="beta", a = 0, b = 0.2,log=FALSE)
Solution

  • Assuming you're using the truncdist package (you should always specify when you're using non-base resources, as there could be a dtrunc() function in more than one non-base package): you need to use shape1 and shape2 as the names of the shape parameters, not a and b

    pdf <- dtrunc(p, spec="beta", shape1 = 0, shape2 = 0.2,log=FALSE)

    This is line with the base R function dbeta (which does use a and b in the Details section, but it's explicit:

    The Beta distribution with parameters ‘shape1’ = a and ‘shape2’ = b has density

              Gamma(a+b)/(Gamma(a)Gamma(b))x^(a-1)(1-x)^(b-1)