Date: Feb 12, 2013 2:16 PM
Author: Derek Goring
Subject: Re: second derivative
On Wednesday, February 13, 2013 5:07:20 AM UTC+13, winnie wrote:

> "aasim Azooz" <aasimazooz@yahoo.com> wrote in message <g2483i$bfa$1@fred.mathworks.com>...

>

> >

>

> > if y=f(x) then the first derivative is

>

> > y1=diff(y)./diff(x)

>

> > The second derivative is

>

> > y2=diff(y1)./diff(x)

>

> > don't forget that the size of y1 is less than the size of y

>

> > by one and the size of y2 is less than the size of y by two

>

> >

>

> > Aasim Azooz

>

> >

>

>

>

> Hi,

>

>

>

> I just looked into computing an approximate second derivative with Matlab and found the answer given by Aasim (above).

>

>

>

> However, shouldn't it rather be:

>

> y2=diff(y1)./diff(x^2) ?

>

>

>

> The answer Aasim gave comes up repeatedly (in similar form) in my web searches, hence I am not sure whether I am making a conceptual error here...

>

> My x values are equally spaced, in case that makes a difference.

>

>

>

> Thanks,

>

> Winnie

Yes, you are making a conceptual error.

Aasim has the correct algorithm.