get_elbow {invivoPKfit}R Documentation

Get an elbow point

Description

Given a set of data specified as two vectors of 'x' and 'y' values, find an elbow point.

Usage

get_elbow(x, y, ...)

Arguments

x

The 'x' values from the data where an elbow point is to be found.

y

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.

Details

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.)

Value

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.

Author(s)

Caroline Ring


[Package invivoPKfit version 2.0.1 Index]