[Gretl-users] zero values

[Riccardo (Jack) Lucchetti]

On Fri, April 20, 2007 17:13, Marco Marini wrote:
>
> Hi,
>   I created an harmonic with the following command:
>   a1=sin(pi*time)
>  where time is a trend series. I expected a zero vector,
>  but the program returns something which is very close to
>  zero but not exactly, as shown in the tabulation
>
>     Obs            b2
>
>   1981:1  1.22461e-016
>   1981:2 -2.44921e-016
>   1981:3  3.67382e-016
>    ...
>  and in the graph, which is not a straight line at y=0.
>
>  I understand this is due to the numerical accuracy at which the program
> works,
>  but I wonder if it's possible to set an option to show 0 whenever
>  values are lower than a fixed level (say 10^-5).

I don't think you really want to do this.

suppose you have

nulldata 200
setobs 1 1 --special
genr time
x = sin(pi*time)

and suppose you set the threshold at 5.0e-14 (arbitrary). You'd end up
seeing stuff like this:

    Obs             x

       1             0
       2             0
       3             0
 ...
     161             0
     162             0
     163   5.19355e-14
     164  -6.27161e-14
     165   7.34967e-14
     166             0
     167             0
     168             0
     169             0
     170             0
     171             0
     172             0
     173             0
     174  -5.68353e-14
     175   6.76159e-14
     176  -7.83965e-14
     177             0
     178             0
     179             0


which is not very nice, is it?

IMHO, anyone who uses gretl should know what the exponential notation
means. I mean, I'm all for user-friendliness, but this is not a
kindergarten.

Riccardo (Jack) Lucchetti
Dipartimento di Economia
Facoltà di Economia "G. Fuà"
Ancona