[Rd] Method dispatch S3/S4 through optimize()

[Roger Bivand]

I have been running into difficulties with dispatching on an S4 class
defined in the SparseM package, when the method calls are inside a
function passed as the f= argument to optimize() in functions in the spdep
package. The S4 methods are typically defined as:

setMethod("det","matrix.csr", function(x, ...) det(chol(x))^2)

that is within setMethod() rather than by name before the setMethod().

When called from within functions passed as the f= argument to optimize, 
the S3 generics for det() and chol() get picked up, not the S4 generics 
for the S4 SparseM classes. This looks for instance like (from 
example(boston)):

> gp2 <- lagsarlm(log(CMEDV) ~ CRIM + ZN + INDUS + CHAS + I(NOX^2) + I(RM^2)
+  +  AGE + log(DIS) + log(RAD) + TAX + PTRATIO + B + log(LSTAT),
+  data=boston.c, nb2listw(boston.soi), method="SparseM")
matrix.csr 
Error in chol(tmp1) : non-numeric argument to chol

(this is the error message in chol.R in base). tmp1 is of class
"matrix.csr", but is being sent to the S3 class (error in function 
sar.lag.mix.f.sM() in R/lag.spsarlm.R). 

sar.lag.mix.f.sM <- function(rho, W, e.a, e.b, e.c, n, quiet)
{
	SSE <- e.a - 2*rho*e.b + rho*rho*e.c
	s2 <- SSE/n
	tmp1 <- asMatrixCsrIrW(W, rho)
cat(class(tmp1), "\n")
	tmp2 <- chol(tmp1)
#	tmp2 <- .cholMatrixCsr(tmp1)
cat(class(tmp2), "\n")
	tmp3 <- (tmp2 at det)^2
cat(tmp3, "\n")
	ret <- (log(tmp3)
		- ((n/2)*log(2*pi)) - (n/2)*log(s2) - (1/(2*s2))*SSE)
	if (!quiet) 
	    cat("(SparseM) rho:\t", rho, "\tfunction value:\t", ret, "\n")
	ret
}


Three further observations:

1) In a simpler case:

> library(spdep)
Loading required package: tripack 
Loading required package: maptools 
Loading required package: foreign 
Loading required package: SparseM 
[1] "SparseM library loaded"
> example(similar.listw)
...
smlr.l> log(det(asMatrixCsrIrW(asMatrixCsrListw(similar.listw(COL.W)), 0.5)))
[1] -1.627660

just works, and the appropriate det() and chol() are found; det() 
dispatches on class "matrix.csr" and finds the right chol() for that 
class - this is the same code context as found in the function passed to 
optimize(); 

2) When the R source file containing the lagsarlm() function, and the
function sent as f= through optimize is sourced(), the appropriate det()
and chol() are found; and

3) When the SparseM R code is modified, and the function defined prior to 
its setMethod (so visible as a function independently of setMethod) and 
called by name rather than as a method, everything works, as it should. 
But this isn't a solution, setMethod() defined methods should dispatch on 
class irrespective of context, I think.

SparseM does not have a namespace, spdep does, but I don't think this is
the issue. I'm pretty sure this isn't an issue with SparseM either,
because of 1).

I've put a copy of the problematic spdep on:

http://reclus.nhh.no/R/spdep/spdep_0.2-24.tar.gz

should that be of any use, the issue is present in both R-2.0.1 and 
R-devel (2004-11-16), SparseM is 0.52. 

I hope that I'm missing something fairly obvious.

Roger

-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Breiviksveien 40, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 93 93
e-mail: Roger.Bivand at nhh.no