Dear list members,
I want to draw surfaces of Dirichlet distributions with different
parameter settings.
My code is the following:
#<begin code>
a1 <- a2 <- a3 <- 2
#a2 <- .5
#a3 <- .5
x1 <- x2 <- seq(0.01, .99, by=.01)
f <- function(x1, x2){
term1 <- gamma(a1+a2+a3)/(gamma(a1)*gamma(a2)*gamma(a3))
term2 <- x1^(a1-1)*x2^(a2-1)*(1-x1-x2)^(a3-1)
term3 <- (x1 + x2 < 1)
term1*term2*term3
}
z <- outer(x1, x2, f)
z[z<=0] <- NA
persp(x1, x2, z,
main = "Dirichlet Distribution",
col = "lightblue",
theta = 50,
phi = 20,
r = 50,
d = 0.1,
expand = 0.5,
ltheta = 90,
lphi = 180,
shade = 0.75,
ticktype = "detailed",
nticks = 5)
#<end code>
It works fine (I guess), except for a1=a2=a3=1. In that case I get the
error: Error in persp.default... invalid 'z' limits.
The z matrix has only elements 2 and NA.
Any ideas are appreciated.
Thank you:
Daniel
University of Pécs
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