From help-octave-request at bevo dot che dot wisc dot edu  Tue Jan 19 01:46:18 1999
Subject: Re: diff(x) question
From: El Jeffo <mirage at cyberdude dot com>
To: Van den Eynde Gert <gvdeynde at SCKCEN dot BE>
CC: help-octave at bevo dot che dot wisc dot edu
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
much.

Jeff