Cubic spline in Matlab works with natural boundary?

I want to make an interpolation with a cubic spline function. And I want to find the coefficients of the polynomials with this function [breaks coefs] = unmkpp(spline(x,y)) . The Matlab function uses natural bouundary or something else?

Answer 1

[Torsten]

By default, MATLAB uses "not-a-knot" condition in end points:

http://www.cs.tau.ac.il/~turkel/notes/numeng/spline_note.pdf

[Iulian Negoiu]

Ok . This is strange . Where I read I understood that the cubic spline works just with secondary derivates. And now we use the third.