Save parameters from optim during iteration procedure

Dear R-users,
I am going to try to be as clearer as possible, showing also an example.
1) I have a function (in my real case it's much more complex)
2) I use "optim" to minimize
3) I want to use as method L-BFGS-B for several reasons
4) I know I could use "trace=6" (in "control") in order to see "live"
the procedure
5) I would like to see separately the values of my parameters during
each iteration (what, on the screen, are the values of X)
6) Hence I would need to know the way of asking R to save somewhere the
values of X during the optimization procedure
7) I have already tried to use "write.table" into the function I want to
minimize (in the example with comments), but it gave me more values that
I would need

Might you know a solution?

EXAMPLE:
###### function
fun <- function(param){
    a <- param[1]
    b <- param[2]
    r <- sqrt(a^2+b^2)
    res <- -10 * sin(r)/r
    #write.table(x=b, file="B.txt", append=TRUE, sep=",",
col.names=FALSE,
    #          row.names=FALSE)

    return(res)
    }

######## optimization procedure
ott <- optim(par=c(-1,1),
      fn =fun,
      method = c("L-BFGS-B"),
      control=c(trace=6)
      )

######### what I would need to save
[...]
X = -0.292893 0.292893
[...]
X = 0.0942275 -0.0942275
[...]
X = -0.00110391 0.00110391
[...]
X = 1.93949e-006 -1.93949e-006
[...]
X = -4.98008e-013 4.98008e-013
[...]



Thanks in advance,
Carlo Giovanni Camarda



Camarda Carlo Giovanni
Max Planck Institute for Demographic Research
Konrad-Zuse-Strasse 1
18057 Rostock, Germany

Tel:  +49 (0)381 2081 172
Fax: +49 (0)381 2081 472
Camarda at demogr.mpg.de




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