diff --git a/vignettes/intro-poped.Rmd b/vignettes/intro-poped.Rmd
index 93891a7..200b79b 100644
--- a/vignettes/intro-poped.Rmd
+++ b/vignettes/intro-poped.Rmd
@@ -82,10 +82,10 @@ packageVersion("PopED")
 ff <- function(model_switch,xt,parameters,poped.db){
   with(as.list(parameters),{
     N = floor(xt/TAU)+1
-    y=(DOSE*Favail/V)*(KA/(KA - CL/V)) * 
+    f=(DOSE*Favail/V)*(KA/(KA - CL/V)) * 
       (exp(-CL/V * (xt - (N - 1) * TAU)) * (1 - exp(-N * CL/V * TAU))/(1 - exp(-CL/V * TAU)) - 
          exp(-KA * (xt - (N - 1) * TAU)) * (1 - exp(-N * KA * TAU))/(1 - exp(-KA * TAU)))  
-    return(list( y=y,poped.db=poped.db))
+    return(list( f=f,poped.db=poped.db))
   })
 }
 ```
@@ -106,10 +106,10 @@ Now we define the residual unexplained variability (RUV) function, in this case
 ```{r}
 feps <- function(model_switch,xt,parameters,epsi,poped.db){
   returnArgs <- ff(model_switch,xt,parameters,poped.db) 
-  y <- returnArgs[[1]]
+  f <- returnArgs[[1]]
   poped.db <- returnArgs[[2]]
  
-  y = y*(1+epsi[,1])+epsi[,2]
+  y = f*(1+epsi[,1])+epsi[,2]
   
   return(list(y=y,poped.db=poped.db)) 
 }