[Rd] uniroot arguments (PR#9140)

[Peter Dalgaard]

trish at maigret.psy.ohio-state.edu writes:

> <<insert bug report here>>
> 
> When invoking "uniroot" with any argument named "u", uniroot exits
> with error: "Error in f(lower, ...) : argument "u" is missing, with no
> default".  This error occurs whether or not "u" determines the root.
> 
> Giving "u" a default value results in garbage from uniroot.
> 
> ## Define a function with a root:
> > test<-function(x,a) (x-a)^3
> 
> ## Find the root:
> > uniroot(test,c(0,1),a=.75)
> $root
> [1] 0.7500141
> 
> $f.root
> [1] 2.793453e-15
> 
> $iter
> [1] 22
> 
> $estim.prec
> [1] 6.103516e-05
> 
> ## All is well.  Change argument "a" to "u":
> > test<-function(x,u) (x-u)^3
> ## Plot it:
> > plot(seq(0,1,by=.1),test(seq(0,1,by=.1),u=.75),type='l')
> 
> ## All is well.  Find the root:
> > uniroot(test,c(0,1),u=.75)
> Error in f(lower, ...) : argument "u" is missing, with no default
> 
> ## Define a new function with the same root:
> > test<-function(x,a,u) (x-a)^3 /u
> ## Plot it:
> > plot(seq(0,1,by=.1),test(seq(0,1,by=.1),a=.75,u=.2),type='l')
> 
> ## All is well.  Find the root:
> > uniroot(test,c(0,1),a=.75,u=.2)
> Error in f(lower, ...) : argument "u" is missing, with no default
> 
> ## Give u a default value:
> > test<-function(x,a,u=.2) (x-a)^3 /u
> ## Find the root:
> > uniroot(test,c(0,1),a=.75,u=.2)
> Error in uniroot(test, c(0, 1), a = 0.75, u = 0.2) :
>         f() values at end points not of opposite sign
> 
> ## Oh, really?
> > test(0,.75,.2)
> [1] -2.109375
> > test(1,.75,.2)
> [1] 0.078125


This is partial matching playing tricks on you. Annoying, but not a bug:


> test<-function(x,a,u=.2) (x-a)^3 /u
> uniroot(test,c(0,1),a=.75,u=.2,upper=1)
$root
[1] 0.7500141

$f.root
[1] 1.396726e-14

$iter
[1] 21

$estim.prec
[1] 6.103516e-05




-- 
   O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
 (*) \(*) -- University of Copenhagen   Denmark          Ph:  (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)                  FAX: (+45) 35327907