R Under development (unstable) (2024-07-17 r86903 ucrt) -- "Unsuffered Consequences"
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> 
> library(ipred)
> suppressWarnings(RNGversion("3.5.3"))
> 
> # check if SdiffKM computes
> # 
> # int_start^stop  (exp(-h*t) - c)^2 dt 
> # 
> # in the correct way 
> 
> # low-level interface needed
> myfoo <- function(times, prob, h, window=0.0001) {
+  .Call("SdiffKM", as.double(c(0, times)), 
+         as.double(c(prob[1], prob)), as.double(c(h,
+         window)), PACKAGE = "ipred")
+ }
> 
> # to compare with
> mexp <- function(start, stop, haz, c=0) {
+   foo <- function(t)
+     exp(-2*haz*t)/(-2*haz) - 2*c*exp(-haz*t)/(-haz) + c^2*t
+   foo(stop) - foo(start)
+ }
>  
> 
> times <- seq(from=0.01, to=8, by=0.01)
> 
> for (myc in c(0,0.5,0.9)) {
+   for (h in c(1,2,3)) {
+     prob <- rep(myc, length(times))   
+     a <- round(mexp(0, max(times), h, c=myc),7)
+     b <- round(myfoo(times, prob, h), 7)
+     stopifnot(all.equal(a,b))
+   }
+ }
> 
> proc.time()
   user  system elapsed 
   1.73    0.31    2.00