[Gretl-users] zero values

[Allin Cottrell]

On Fri, 20 Apr 2007, Marco Marini wrote:

>  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).

You can construct a series that's screened for computer-numerical 
noise if you wish, for example:

tmp = sin(pi*time)
NOISE = 1.99e-14
a1 = tmp * (abs(tmp) > NOISE)

Allin Cottrell