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Re: diff(x) question

From: El Jeffo
Subject: Re: diff(x) question
Date: Tue, 19 Jan 1999 07:46:50 +0000

> Diff computes forward differences. Not the derivative. If you want to
Ah that's why I get back one less term right? 

> approximate the derivative by using forward differences you have to
> divide by the step h with which you make your function discrete.
> In this case h = .1
> df          f(t+h) - f(t)
> -- (t) =~  --------------- + O(h)
> dt                h

Um, okay is there a function that does this and returns a vector/array
for that?  If not, I'm at a loss on how to do this nicely in the
future... I guess I can make my own function like 

result = mydiff(x(t)) ?

do I write it like:

function mydiff(f)
  Uh..... good grief, I can't even figure out where to start

I mean I can write it in C or like perl, but I dunno how to do it 
in matlab or octave... is this something trivial?  

Actually this is for an assignment for a class I'm taking, but they
want it in matlab.  One of the problems speced that we use the diff()
function in matlab, does the octave version work the same?  Otherwise,
I guess I'll go shell out the money for matlab... just trying to
see how much octave can do in place of matlab.  

Hey thanks for all the help and I understand if this is asking too


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