nls2 <- function(formula, data = parent.frame(), start, control = nls.control(),
	algorithm = c("default", "plinear", "port", "brute-force", "grid-search", "random-search"), ...,
	all = FALSE) { 

	L <- (list(formula = formula, data = data, control = control))
	if (!missing(start)) { 
		if (inherits(start, "nls")) {
			start <- coef(start)
			# remove names that begin with a dot (generated by plinear)
			start <- start[grep("^[^.]", names(start))]
		}
		L$start <- start
	}
	finIter <- NROW(L$start)
	L <- append(L, list(...))
	algorithm <- match.arg(algorithm)
	if (algorithm == "grid-search") algorithm <- "brute-force"
	call <- match.call()
	if (algorithm == "brute-force" || algorithm == "random-search") {
	   nls <- function(formula, data, start, ...) {
	      nlsModel <- stats:::nlsModel
	      environment(nlsModel) <- environment()
	      #  disable nlsModel gradient error
	      stop <- function(...) {
	        msg <- "singular gradient matrix at initial parameter estimates"
	        if (list(...)[[1]] == msg) return()
	        stop(...)
	      }
	      structure(list(m = nlsModel(formula, data, start), 
	         call = call,
	         convInfo = list(isConv = TRUE, finIter = finIter,
			finTol = NA)), class = "nls")
	   }
	} else L$algorithm <- algorithm

	if (missing(start)) return(do.call(nls, L))
	else L$start <- as.data.frame(as.list(start))

	if (NROW(L$start) == 1) return(do.call(nls, L))

	if (NROW(L$start) == 2) {
	   if (algorithm == "brute-force") {
		rng <- as.data.frame(lapply(start, range))
		mn <- rng[1,]
		mx <- rng[2,]
		# k is number of points in each dimension to take
		# so that cross product is close to maxiter points.
		k1 <- pmax(ceiling(sum(mx > mn)), 1)
		k <- pmax(ceiling(control$maxiter ^ (1/k1)), 1)
		DF <- as.data.frame(rbind(mn, mx, k))
		# L$start <- expand.grid(by(DF, 1:NROW(DF), do.call, what = 
			#function(from, to, len) seq(from, to, length = len)))
		finIter <- k^k1
		L$start <- expand.grid(lapply(DF, 
			function(x) seq(x[1], x[2], length = x[3])))
	   } else {
		finIter <- control$maxiter
		u <- matrix(runif(finIter * NCOL(start)), NCOL(start))
		L$start <- t(u * unlist(start[1,]) + (1-u) * unlist(start[2,]))
		L$start <- as.data.frame(L$start)
		names(L$start) <- names(start)
	   }
		
	}

	result <- apply(L$start, 1, function(start) {
		L$start <- start
        # 1/29/2008 changes
		xx <- try(do.call(nls, L))
        yy <- if (inherits(xx, "try-error")) NA else xx
        print(yy)
        yy
	})
	if (all) result else {
		# ss <- lapply(result, function(x) if (identical(x, NA)) NA else sum(resid(x)^2))
		# deviance gives the sum of squares of the residuals
		ss <- lapply(result, function(x) if (identical(x, NA)) NA 
			else deviance(x))
		result[[which.min(ss)]]
	}
}