# [Rcpp-devel] Help for call R function

bbonit at tin.it bbonit at tin.it
Fri Jun 15 22:04:01 CEST 2012

``` Hello to everyboby  Im Gianluca ....and i m a statistic student.
I have one problem that i think  Dirk or some one  "good like dirk"  could help to resolve  :

iI would like to implement this  following function in R code  into inline code with Rccp plugin :

MHWG<-function (logpost, start, n.iter, burn, thin, scale, ...)
{
pb <- txtProgressBar(min = 0, max = n.iter, style = 3)
p = length(start)
vth = array(0, dim = c(n.iter/thin, p))
f0 = logpost(start, ...)
arate = array(0, dim = c(1, p))
th0 = start
for (i in (-burn):n.iter) {
setTxtProgressBar(pb, i)
for (j in 1:p) {
th1 = th0
th1[j] = th0[j] + rnorm(1) * scale[j]
f1 = logpost(th1, ...)
u = runif(1) <= min(exp(f1 - f0),1)
th0[j] = th1[j] * (u == 1) + th0[j] * (u == 0)
f0 = f1 * (u == 1) + f0 * (u == 0)
vth[floor(i/thin), j] = th0[j]
arate[j] = arate[j] + u
}
}
arate = arate/n.iter
stuff = list(par = vth, accept = arate)
return(stuff)
}

So  one argument of MHWG   is   logpost  and  is a R function with argument par where  par iso ne vector ....   for example logpost(par)   Logpost<-function(par) { ...................} (in r code).
How can i call  teh logpost function into the inline rccp code . In the MHWG  there is a difference  f1-f0    where fi=logpost(par1)  e f0=logpost(par 2)  for exemple.
help me please to implemet  my problem   ...and  also i m "open" about  suggestion for implemeting  the function
Sorry  for all noise and thank also for the past mail that  help me to learn more about  programming
Best regards... sorrry fo rmy bad English

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