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winnie
Posts:
14
Registered:
5/20/09
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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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