How to obtain inflection points for a curve ?

We want to find points where curve changed its slop and i attached curve .mat file.

Answer 1

[Walter Roberson]

use gradient() to take numeric derivative. Use gradient() again to get second derivative. Search the second derivative for zeros or sign changes.

[Surendra Ratnu]

There are many points but i want few points among. I showed in the image in green colour points for samples. I need only these points for given curve. Can you tell me how to do that.