R Under development (unstable) (2024-06-20 r86796 ucrt) -- "Unsuffered Consequences"
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> require(salad)
Loading required package: salad

Attaching package: 'salad'

The following object is masked from 'package:stats':

    dnorm

> set.seed(1)
> x <- dual( runif(25) )
> A <- matrix( rep(x, 25) + runif(25*25), 25, 25)
> 
> # vA <- value(A)
> # dA <- d(A)
> 
> # vx <- value(x)
> # dx <- d(x)
> 
> f1 <- function(A, x) (A %*% x)@d
> 
> f2 <- function(A, x) {
+   vA <- A@x
+   vx <- x@x
+   dA <- unclass(A@d)
+   dx <- unclass(x@d)
+   B <- vA %*% vx
+   dB <- vector("list", length(dA))
+   for(k in seq_along(dB)) dB[[k]] <- dA[[k]] %*% vx + vA %*% dx[[k]]
+   # this is 0.2 - 0.5 µs 
+   # names(dB) <- names(dA)
+   # class(dB) <- "differential"
+   # this takes 15 µs !
+   # A@x <- B
+   # A@d <- dB
+   # A@d
+   # this is still 3 µs
+   # BB <- salad:::fastNewDual(B, dB)
+   # BB@d
+   dB
+ }
> 
> f3 <- function(A, x) matrixprod_dd(A, x)@d
> 
> Z1 <- f1(A, x)
> Z2 <- f2(A, x)
> Z3 <- f3(A, x)
> test <- TRUE
> for(i in 1:5) test <- test & all(Z1[[i]] == Z2[[i]])
> for(i in 1:5) test <- test & all(Z1[[i]] == Z3[[i]])
> stopifnot(test)
> 
> # mb <- microbenchmark::microbenchmark(f1(A, x), f2(A, x), f3(A, x), times = 1e4)
> # print(mb)
> 
> 
> proc.time()
   user  system elapsed 
   0.23    0.06    0.28