Given a set of data specified as two vectors of `x` and `y` values, find an elbow point.
get_elbow(x, y, ...)A list with two named numeric scalar elements, `x` and `y`. `x` contains the `x` value at the elbow point. `y` contains the `y` value at the elbow point. The elbow point is *not* necessarily one of the input data points; it may be interpolated.
The `x` values from the data where an elbow point is to be found.
The `y` values from the data where an elbow point is to be found.
Optional: additional arguments that will be passed to [stats::approx()] if it is used.
Caroline Ring
This is a helper function for [get_starts()] to find elbow points.
Given a set of (x,y) data points, an "elbow point" can be defined by drawing a line connecting the points for minimum and maximum x, and then finding the x value of the observation where the distance to that line is greatest.
[get_starts()] uses elbow points as a way to automate separation of concentration-time data into different kinetic phases in order to calculate starting points for fitting TK model parameters. For example, if concentration-time data are described by a two-compartment TK model, then early and late elimination phases will be separated by an elbow point. This helper function finds the elbow points. (When this function is called from [get_starts()], `x` will be a vector of time values, and `y` will be a vector of log-transformed dose-normalized concentration values.)