Question

What is the algorithm of rchisq() function in R?

I am trying to build my myrchisq(), can anyone build the function that will give me the same result as rchisq()?

Note: I don't need ncp = 0

I just need myrchisq = function(n, df){}

Answer 1

I will develop the function using the help of rnorm() function in R. I will assume the non- centrality parameter as 0.

Following is the code. If you run the code, you will get the answer.

###############################################################################

library(MASS)

mychisq=function(sampsize,df)

{

rs=array(dim=1)

for(i in 1:sampsize)

{

x=mvrnorm(1,mu=rep(0,df),Sigma=diag(1,df))

rs[i]=t(x)%*%x

}

return(rs)

}

#To compare mychisq() with rchisq()

par(mfrow=c(1,2))

hist(mychisq(10000,5),freq=F)

hist(rchisq(10000,5),freq=F)

############

After running the code, we will see that both are giving same histogram.

If you do not get anything in this solution, please put a comment and I will help you out. Do not give a downvote instantly. It is a humble request. If you like my answer, please give an upvote.