With main R releases only happening yearly in spring, now is good time to consider *and* discuss new features for what we often call "R-devel" and more officially is R Under development (unstable) (.....) -- "Unsuffered Consequences"
Here is one such example I hereby expose to public scrutiny: A few minutes ago, I've committed the following to R-devel (the 'trunk' in the svn repository for R): ------------------------------------------------------------------------ r62834 | maechler | 2013-05-30 10:01:33 +0200 (Thu, 30 May 2013) | 1 line Changed paths: M doc/NEWS.Rd M src/library/stats/NAMESPACE M src/library/stats/R/nlm.R M src/library/stats/man/uniroot.Rd M tests/Examples/stats-Ex.Rout.save new "safe" uniroot() =: unirootS() [may change; see R-devel e-mail] ------------------------------------------------------------------------ The help file says ‘unirootS()’ is a “safe” version of ‘uniroot()’, built on ‘uniroot()’, also useful as drop-in replacement of ‘uniroot()’ in some cases. “Safe” means searching for the correct ‘interval = c(lower,upper)’ if ‘sign(f(x))’ does not satisfy the requirements at the interval end points; see the ‘Details’ section. We've had this function, called safeUroot() in our package copula for a while now, where an earlier not-exported version has been in my package nor1mix even longer. When I was tempted to introduce it into yet another CRAN package I maintain, I decided that this may be a sign that such a simple [ utility for / generalization of ] uniroot() should probably rather be added to R itself. The function definition, also visible in R's devel.sources, at the bottom of https://svn.r-project.org/R/trunk/src/library/stats/R/nlm.R , shows that unirootS() is a wrapper for uniroot() and is in principle 100% back compatible to uniroot() itself for all the cases where f(lower) and f(upper) are of differing sign and hence uniroot() does not give a quick error. unirootS() just has three new optional arguments, all with their defaults set such as to remain uniroot() compatible. So, one option instead of the currently commited one would be to adopt unirootS() as "the new uniroot()" and rename current uniroot to .uniroot() {and still export both}. The capital "S" in the function name and the 'Sig' name is of course quite a matter of taste, and this case corresponds to my taste, but even that is part of the RFC. unirootS <- function(f, interval, ..., lower = min(interval), upper = max(interval), f.lower = f(lower, ...), f.upper = f(upper, ...), Sig = NULL, check.conv = FALSE, tol = .Machine$double.eps^0.25, maxiter = 1000, trace = 0) { if ( is.null(Sig) && f.lower * f.upper > 0 || is.numeric(Sig) && (Sig*f.lower > 0 || Sig*f.upper < 0)) { if(trace) cat(sprintf("search in [%g,%g]%s", lower, upper, if(trace >= 2)"\n" else " ... ")) Delta <- function(u) 0.01* pmax(1e-7, abs(u)) ## Two cases: if(is.null(Sig)) { ## case 1) 'Sig' unspecified --> extend (lower, upper) at the same time delta <- Delta(c(lower,upper)) while(isTRUE(f.lower*f.upper > 0) && any(iF <- is.finite(c(lower,upper)))) { if(iF[1]) f.lower <- f(lower <- lower - delta[1]) if(iF[2]) f.upper <- f(upper <- upper + delta[2]) if(trace >= 2) cat(sprintf(" .. modified lower,upper: (%15g,%15g)\n", lower,upper)) delta <- 2 * delta } } else { ## case 2) 'Sig' specified --> typically change only *one* of lower, upper ## make sure we have Sig*f(lower) < 0 and Sig*f(upper) > 0: delta <- Delta(lower) while(isTRUE(Sig*f.lower > 0)) { f.lower <- f(lower <- lower - delta) if(trace) cat(sprintf(" .. modified lower: %g\n", lower)) delta <- 2 * delta } delta <- Delta(upper) while(isTRUE(Sig*f.upper < 0)) { f.upper <- f(upper <- upper + delta) if(trace) cat(sprintf(" .. modified upper: %g\n", upper)) delta <- 2 * delta } } if(trace && trace < 2) cat(sprintf("extended to [%g, %g]\n", lower, upper)) } if(!isTRUE(f.lower * f.upper <= 0)) stop("did not succeed extending the interval endpoints for f(lower) * f(upper) <= 0") if(check.conv) { r <- tryCatch(uniroot(f, ..., lower=lower, upper=upper, f.lower=f.lower, f.upper=f.upper, tol=tol, maxiter=maxiter), warning = function(w)w) if(inherits(r, "warning")) stop("convergence problem in zero finding: ", r$message) else r } else uniroot(f, ..., lower=lower, upper=upper, f.lower=f.lower, f.upper=f.upper, tol=tol, maxiter=maxiter) } ----------- As said, your comments are very welcome! Note that I'm less interested in variations which gain 10-20% in speed benchmarks, rather I'd appreciate proposals for changes that give a "better" (in your sense) user interface. Martin Maechler, ETH Zurich ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel