Dear both, I have just found that names are treated in the same way in optim() depending on the optimization method. The example below shows the difference between the Brent method and the L-BFGS-B method. f <- function(x){ y <- x^2;names(y) <-"f(x)";y} optim(10, f, method="Brent", lower=-1, upper=10)$value optim(10, f, method="L-BFGS-B", lower=-1, upper=10)$value z <- 10 names(z) <- "x" z optim(z, f, method="Brent", lower=-1, upper=10)$par optim(z, f, method="L-BFGS-B", lower=-1, upper=10)$par Do you obtain the same behavior? I?m using R version 3.2.1 (2015-06-18) Platform: x86_64-apple-darwin13.4.0 (64-bit) Running under: OS X 10.9.5 (Mavericks) locale: [1] fr_FR.UTF-8/fr_FR.UTF-8/fr_FR.UTF-8/C/fr_FR.UTF-8/fr_FR.UTF-8 attached base packages: [1] stats graphics grDevices utils datasets methods base loaded via a namespace (and not attached): [1] tools_3.2.1 Kind regards, CD --------------------------------------- Christophe Dutang LMM, UdM, Le Mans, France web: http://dutangc.free.fr