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

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

On Mon, 2007-10-22 at 13:51 +0200, Juergen Wieferink wrote:
> Well, AFAICS it has become possible in 4.3, though not very easily
> accessible.
>
> There is a new assignment operator (and a comma operator), so you
> can plot something like:
>
> old_x =3D NaN
> plot 'test.dat' using 1:(dx=3D$1-old_x,old_x=3D$1,dx)
>
> This only works with data file plotting.  You can use the '+' pseudo
> file for fitted data (though I would recommend the analytic
> derivative in this case).  For smoothed curves, plot the results
> into a table file (help set table) and use this file as given
> above.
>
> -- Completely untested --
>
> Juergen


On Mon, 2007-10-22 at 16:26 +0200, pl...@pi... wrote:

> Delta y / Delta x =3D y(row+1)-y(row)/(x(row+1)-x(row)).
>
> sorry I did reply to this one but it went to Levente only not the list.
>
> this sort of trivial task lends itself nicely to the new assign feature
> (only in CVS AFAIK) and is exactly the sort of thing I had in mind when=
 I
> requested it.
>
> check out the syntax since it is still being developed and may change.
>


Thanks J=FCrgen and Peter!

I will try the assignment operator, it sounds promising. This was
exactly my impression, that something new was introduced to gnuplot,
allowing for (sort of) simple differentiation, only I did not remember
exactly which command.

Concerning the spline differentiating question: I am aware that splines
can cause unwanted oscillations, but in the past I was succesfully using
acsplines with weights carefully chosen to approximate the curve I would
draw by hand through the experimental data. Sometimes it is faster this
way than trying to find a good function and fit it with the
Marquardt-Levenberg method (I often don't know exactly which function
describes the experimental behaviour -- e.g. in complex biological
systems).

Levente