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Topic: second derivative
Replies: 5   Last Post: Feb 12, 2013 2:16 PM

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winnie

Posts: 14
Registered: 5/20/09
Re: second derivative
Posted: Feb 12, 2013 11:07 AM
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"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



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