The following code will get me a curve plot: cutoff <- seq(1,7,0.25) Sensitivity <- 1 - pnorm(cutoff, 5, 0.8) Specificity <- pnorm(cutoff, 3, 1.2) plot(1-Specificity,Sensitivity,main = "ROC curve",type = "o") How do I get a gradient of a particular point on that curve? Any packages/functions allow me to do that? Thank you -- View this message in context: http://r.789695.n4.nabble.com/An-issue-regarding-to-gradient-tp3893401p3893401.html Sent from the R help mailing list archive at Nabble.com.
An issue regarding to gradient
2 messages · luke1022, David Winsemius
On Oct 11, 2011, at 6:02 AM, luke1022 wrote:
The following code will get me a curve plot: cutoff <- seq(1,7,0.25) Sensitivity <- 1 - pnorm(cutoff, 5, 0.8) Specificity <- pnorm(cutoff, 3, 1.2) plot(1-Specificity,Sensitivity,main = "ROC curve",type = "o") How do I get a gradient of a particular point on that curve?
First you need to define what you mean by "gradient at a point" when the gradient is discontinuous at each point. Is this a numerical example and you want to take the means of the slopes on either side, (rather like the definition of the Dirac function at x=0) ... in whiich case these are the slopes _between_not_at_ the points: diff(Specificity)/diff(1-Sensitivity) or ... is this a homework problem and you are being asked to use the knowledge that those (Sensitivity, Specificity) points came from particular pnorm functions?
David Winsemius, MD West Hartford, CT