Monotonicity function. Internal error?

Good morning!

I have a lot of variables with longitudinal data and I have to select the best of those. One of the things that I'm taking into account is their monotonicity. I'm using montonocity function (sign method).

I've kept the individual values that MAtlab calculate just to show on a plot the meaning of perfect monotonicity. I've plotted all the rows on my table that have monotonicity=1, but, surprisingly I can clearly see a couple of series that are not monotonous and still have a value of monotonicity=1...

Do you know if the function is doing any kind of approximation inside?

Thank you!

Regards,

MartaJ

Answer 1

[Steven Lord]

If you're using the monotonicity function in Predictive Maintenance Toolbox, see the Algorithms section on that documentation page for a description of what each of the different methods does to compute monotonicity.