Nothing
# Computation of EWMA ARLs (variance monitoring) based on ln S^2
lns2ewma.arl <- function(l, cl, cu, sigma, df, hs=NULL, sided="upper", r=40) {
#mitte <- -1/df - 1/3/df^2 + 2/15/df^4 # approx following Crowder/Hamilton
mitte <- log(2/df) + digamma(df/2)
if ( is.null(cl) ) cl <- mitte
if ( is.null(cu) ) cu <- mitte
if ( is.null(hs) ) hs <- mitte
if ( l<=0 || l>1 ) stop("l has to be between 0 and 1")
#if ( cu < mitte ) stop(paste("cu has to be larger than", mitte))
#if ( cl > mitte ) stop(paste("cl has to be smaller than", mitte))
if ( sigma<=0 ) stop("sigma must be positive")
if ( df<1 ) stop("df must be larger than or equal to 1")
if ( hs<cl-1e-9 | hs>cu+1e-9 ) stop("wrong headstart")
ctyp <- pmatch(sided, c("upper", "lower", "two")) - 1
if ( is.na(ctyp) ) stop("invalid ewma type")
if ( r<10 ) stop("r is too small")
arl <- .C("lns2ewma_arl", as.integer(ctyp), as.double(l),
as.double(cl), as.double(cu), as.double(hs),
as.double(sigma), as.integer(df), as.integer(r),
ans=double(length=1),PACKAGE="spc")$ans
names(arl) <- "arl"
return (arl)
}
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