Linear piecewise interpolation problem

Hello. I would like to make a interpolation to my data that I obtain from qqplot in MATLAB . I would like to have eg. three interpolation best fitted lines. Here is my data in represented by qqplot. Any ideas how to simply do this?

Answer 1

[Matt J]

http://www.mathworks.com/matlabcentral/fileexchange/25872-free-knot-spline-approximation

[Jonasz]

I need something else. I need to put a lines into this plot so it will show me three different lines like this

But how to code this?

[Matt J]

Once BSFK gives you the pp-form just evaluate it at 2 points between each of the knots. Then you can use polyfit() to fit a line to each pair of points and plot.

[Jonasz]

Could you explain it more ? I don't understand it. What is my input of bsfk ? I have only one column of values.

[Matt J]

The documentation for bsfk should explain everything.