R devel - Dec 2011 - Detecting typo in function argument

With some chagrin after spending a couple of hours trying to debug a script, I
realized I
had typed in something like

ans<-optimx(start, myfn, mygr, lower<-lo, upper=up)

that is, the "<-" rather than "=". The outcome on my
machine was a non-obvious error
several layers deep in the call stack. For info, optim() seems to stop much more
quickly.

The error is "obvious", but I'm wondering if there is a simple way
to trap or warn of it.
For completeness, I include the commands I used to force the error. Note that it
will only
work fully with the latest (R-forge) version of optimx/optfntools because of the
form of
gr="gfwd" that allows a choice of different numerical gradient
routines.

This is a curiosity rather than a necessity, but if there is a simple way to
check, I'll
put it in my codes.

Cheers,

JN

rm(list=ls())
start<-rep(3,6)
lo<-rep(2,6)
up<-rep(4,6)
flb <- function(x)
    { p <- length(x); sum(c(1, rep(4, p-1)) * (x - c(1, x[-p])^2)^2) }
ans<-optim(start, flb, lower=lo, upper=up)
ans
ans<-optim(start, flb, lower<-lo, upper=up)
ans
ans1<-optim(start, flb, lower<-lo, upper=up)
ans1
require(optimx)
ans1x<-optimx(start, flb, lower<-lo, upper=up)
ans1x<-optimx(start, flb, gr="gfwd",lower<-lo, upper=up)
ans1<-optim(start, flb, gr=NULL,lower<-lo, upper=up)

This is valid syntax, so what should we check for?.

Uwe


On 12.12.2011 22:10, John C Nash wrote:
> With some chagrin after spending a couple of hours trying to debug a
script, I realized I
> had typed in something like
>
> ans<-optimx(start, myfn, mygr, lower<-lo, upper=up)
>
> that is, the "<-" rather than "=". The outcome on my
machine was a non-obvious error
> several layers deep in the call stack. For info, optim() seems to stop much
more quickly.
>
> The error is "obvious", but I'm wondering if there is a
simple way to trap or warn of it.
> For completeness, I include the commands I used to force the error. Note
that it will only
> work fully with the latest (R-forge) version of optimx/optfntools because
of the form of
> gr="gfwd" that allows a choice of different numerical gradient
routines.
>
> This is a curiosity rather than a necessity, but if there is a simple way
to check, I'll
> put it in my codes.
>
> Cheers,
>
> JN
>
> rm(list=ls())
> start<-rep(3,6)
> lo<-rep(2,6)
> up<-rep(4,6)
> flb<- function(x)
>      { p<- length(x); sum(c(1, rep(4, p-1)) * (x - c(1, x[-p])^2)^2) }
> ans<-optim(start, flb, lower=lo, upper=up)
> ans
> ans<-optim(start, flb, lower<-lo, upper=up)
> ans
> ans1<-optim(start, flb, lower<-lo, upper=up)
> ans1
> require(optimx)
> ans1x<-optimx(start, flb, lower<-lo, upper=up)
> ans1x<-optimx(start, flb, gr="gfwd",lower<-lo, upper=up)
> ans1<-optim(start, flb, gr=NULL,lower<-lo, upper=up)
>
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