Re: Some way to differentiate (1st order derivative)?

[Levente <ln...@dr...>]

On Wed, 2007-10-24 at 14:45 +0200, pl...@pi... wrote:
> On Wed, 24 Oct 2007 13:43:22 +0200, Levente Nov=C3=A1k =20
> <ln...@dr...> wrote:
> > First of all, thanks to everybody who helped me! I succeeded in
> > approximating the differential of data files the following way, using
> > J=C3=BCrgen's example:
> >
> > # Approximation of the first derivative of x-y data
> > # by the method: (y(n)-y(n-1))/(x(n)-x(n-1))
> >
> > old_x =3D NaN
> > old_y =3D NaN
> > plot 'something.dat' using 1:(dx=3D$1-old_x,dy=3D$2-old_y,old_x=3D$1,ol=
d_y=3D
> > $2,dy/dx)
> >
> > Just to let know to whom it may be useful. Maybe a small demo file coul=
d
> > be written to demonstrate its use (I am pleased to post such a demo if
> > this is OK).
> >
> Glad you found this feature useful.
>=20
> It's quite new so it needs some different uses to see if does all that's =
=20
> needed, thanks.
>=20
> if you want to post that as an example it should probably by plotting =20
> against ($1+old_x)/2 to prevent a shift in the position of the derivative=
.
>=20

You are absolutely right, the x values need to be corrected (only I had
so many datapoints that this shift was very small in my initial
example). I will adapt the formula accordingly.

Levente