R/temp to xy m2.R

In AkselA/R-kelvincol:

#' @export
K2xy2 <- function(K) {
	# US patent 7024034, Kim et al. 2006
	# This approximation is reasonably accurate for K > 1700 & K < 25000
	y <- x <- numeric(length(K))
	
	sK1 <- K <= 4000
	K1 <- K[sK1]
	x[sK1] <- -0.2661239 * (10^9) / (K1^3) -
	           0.2343580 * (10^6) / (K1^2) +
	           0.8776956 * (10^3) / (K1) +
	           0.1799100

	sK2 <- K > 4000
	K2 <- K[sK2]
	x[sK2] <- -3.0258469 * (10^9) / (K2^3) +
	           2.1070379 * (10^6) / (K2^2) +
	           0.2226347 * (10^3) / (K2) +
	           0.2403900

	sx1 <- K <= 2222
	x1 <- x[sx1]
	y[sx1] <- -1.10638140 * (x1^3) -
	           1.34811020 * (x1^2) +
	           2.18555832 * (x1) -
	           0.20219683

	sx2 <- K > 2222 & K <= 4000
	x2 <- x[sx2]
	y[sx2] <- -0.95494760 * (x2^3) -
	           1.37418593 * (x2^2) +
	           2.09137015 * (x2) -
	           0.16748867

	sx3 <- K > 4000
	x3 <- x[sx3]
	y[sx3] <-  3.08175800 * (x3^3) -
	           5.87338670 * (x3^2) +
	           3.75112997 * (x3) -
	           0.37001483
	
	cbind(x, y)
}