Find slope signal change

Hello, I have this graph and I want to find out when does the slope changes from negative to positive around index ~100, for each group (younger and older), using polyfit.

Each line in the plot is a matrix column (ignore the shaded area, that's the standard error of the mean).

Answer 1

[Star Strider]

The ischange function (introduced in R2017b) is helpful here.

Answer 2

[KSSV]

https://www.mathworks.com/matlabcentral/answers/410698-find-time-of-slope-change

https://www.mathworks.com/matlabcentral/answers/168517-how-can-i-find-slope-sign-change-of-a-signal

mathworks.com/matlabcentral/answers/168517-how-can-i-find-slope-sign-change-of-a-signal