curve fitting toolbox

I'm programming in matlab and using curve fitting toolbox to fit my data. I need to evaluate the 1th derivative of my curve in some data point. Do you know how I can do it in my code? I need to use 'cubic spline (interpolant) fitting'.

Answer 1

[Sarah Wait Zaranek]

The curvefit object you get out of curvefitting tool will allow you to take a derivative at a point using the differentiate method.

See code below. I generated a fit using the command line but it is the same thing you can get out of the curvefitting toolbox.

load census
f2 = fit(cdate,pop,'cubicinterp');
fx = differentiate(f2, 0.2)

[Sarah Wait Zaranek]

Aside -- your name and mine are quite similar.

[SARAH ZAVAREH]

Great! Thank you.

But another duestion: Do you know how I can find in which points 1th derivative is equal to zero? (how we can solve first derivative equation?)

p.s. yeah our names are the same :D

Answer 2

[SARAH ZAVAREH]

Do you know how I can find in which points 1th derivative is equal to zero? (how we can solve first derivative equation?)

[Sarah Wait Zaranek]

If you have the optimization toolbox, fzero probably would be ideal.

http://www.mathworks.com/access/helpdesk/help/techdoc/ref/fzero.html

[SARAH ZAVAREH]

Thanks alot for your useful helps :)