Bilinear Fit

Fit two intersecting straight lines to a set of x,y data points.

bilinearFit.m is a function that fits two intersecting straight lines to a set of x,y data points. The slopes and intercepts are chosen to minimize the sum squared error in the y-direction between the data and the corresponding line. The function calls lsqnonlin(), which is in the Optimization Toolbox.

Usage: [a0,a1,b0,b1,x0]=bilinearFit(x,y)

Fitting function:

if (red line in figure below)

if (blue line in figure below)

where is the x-coordinate of the intersection.

The script bilinearFitTest.m demonstrates the use of bilinearFit.m, and it displays results on the console and in a plot.

Reference: Josephson MD, Rose WC, Knight CA (2019). Evidence of bilinearity in the relationship between rate of neuromuscular excitation and rate of force development. Journal of Electromyography and Kinesiology 49: 102355. https://doi.org/10.1016/j.jelekin.2019.102355