Hello Everyone,

I am a MS students in the Department of Statistics, Biostatistics & Informatics, in University of Dhaka, Bangladesh. Recently, I am doing thesis on "D-optimal Designs for Regression models in Biostatistics". In my thesis work, I am having problem with a particular program where I need to replace each element of a vector one by one by every element of another seq (which is of higher length than that of the vector), and then calculated a quantity from each of the resulting vector and compare them. I have written the following program, but I think it is not running correctly, Can anyone please correct this Please!


 dopt<-function(beta)
 {
 set.covar<-seq(-1,1,0.001)
 n<-length(set.covar)
 xi<-sample(set.covar,5)
 ## start of information loop
 infor<-function(xi)
 {
 mu<-exp(t(xi)*beta)/(1+exp(t(xi)*beta))
 mui<-mu%*%t(1-mu)
 xmui<-mui%*%t(xi)
 info<-xmui%*%xi
 }
 ## end of information loop
 info<-infor(xi)
 ##start of loop to replace every element of x (i loop)
 for(i in 1:5)
 {
 ## start of a loop to replace each element of xi with every element of set.covar (j loop)
 for(j in 1:n)
 {
 x<-xi
 xi<-replace(x,i,set.covar[j])
 infoi<-infor(xi)
 info<-ifelse(infoi>info,c(infoi,return(xi)),c(info,return(x)))
 } ## end of j loop
 } ## end of i loop
 } ## end of mainloop (dopt)


Please help me with the loop.

With best regards,

Farzana.
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