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Re: Derivation with Octave


From: Ben Abbott
Subject: Re: Derivation with Octave
Date: Tue, 4 Mar 2008 08:03:13 -0500


On Mar 4, 2008, at 7:36 AM, Julien Martin wrote:
2008/3/2, Ben Abbott <address@hidden>:
On Mar 2, 2008, at 8:32 AM, Julien Martin wrote:

> Hello,
> I am a beginner to Octave and would like to perform derivation on
> some functions. Can anyone please help? What is the syntax of the
> arguments of the differenciate function?
> Thanks in advance,
> Julien.


Octave a numerical (not a symbolic) computational tool. If you are
looking for symbolic derivatives, please consider Maxima.

For numerical derivatives, there are many methods to accomplish that
numerically.

Given you have a pair of vectors, x & y, where y is dependent upon x.

   dydx = diff (y) ./ diff (x);
   xc = x(1:end-1) + diff(x)/2;
   dydx = interp1 (x(n), dydx, xc, "linear", "extrap");

If the function, y, may be accurately represented by a polynomial of
order N

   dydx = polyval ( polyder ( polyfit (x, y, N)), x);

Ben

Hi there,
I tried Maxima and I find it awesome (just like Octave).
However, can any of you please explain to me the difference between numerical and symbolic calculus?
When do I use Octave and when do I use Maxima?
Thanks in advance,
Julien.


"Numerical" refers to calculations, and "symbolic" refers to symbols ... I'm not try to be cheeky, but the difference are quite apparent even on a superficial level.

Octave, Xcel, and even a calculator each are able to do numerical calculations.

The symbolic derivative of "2*x^2 - 4*x + 1" is "4*x - 4".

Ben


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