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[BUGZILLA #14384] Problem with NLSstClosestX; and suggested fix #3974

Closed MichaelChirico closed 4 years ago

MichaelChirico commented 4 years ago

I sent this to R-help sometime in 2009, but I guess it wasn't noticed.

Problem is demonstrated with this code, intended to find the approximate 'x' at which the 'y' is midway between the left and right asymptotes. This particular data set returns NA, which is a bit silly! -------------- sXY <- structure(list(x = c(0, 24, 27, 48, 51, 72, 75, 96, 99), y = c(4.98227, 6.38021, 6.90309, 7.77815, 7.64345, 7.23045, 7.27875, 7.11394, 6.95424)), .Names = c("x", "y"), row.names = c(NA, 9L), class = c("sortedXyData", "data.frame")) a <- NLSstLfAsymptote(sXY) d <- NLSstRtAsymptote(sXY) NLSstClosestX(sXY, (a+d)/2) ------------------------ I think the problem arises when the target y value is exactly equal to one of the y values in sXY and can be fixed by trapping that situation thus: -------------------- NLSstClosestX.sortedXyData <- function (xy, yval) { deviations <- xy$y - yval if (any(deviations==0)) xy$x[match(0, deviations)] else { # new line inserted if (any(deviations <= 0)) { dev1 <- max(deviations[deviations <= 0]) lim1 <- xy$x[match(dev1, deviations)] if (all(deviations <= 0)) { return(lim1) } } if (any(deviations >= 0)) { dev2 <- min(deviations[deviations >= 0]) lim2 <- xy$x[match(dev2, deviations)] if (all(deviations >= 0)) { return(lim2) } } dev1 <- abs(dev1) dev2 <- abs(dev2) lim1 + (lim2 - lim1) * dev1/(dev1 + dev2) } # new line inserted } -------------------

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MichaelChirico commented 4 years ago

I get NaN ... division by zero.

Changed for R 2.12.0.

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