[Scilab-users] Insufficient documentation of interp1

[Federico Miyara]

Samuel,

Thanks for your comments, which encouraged me to submit bug #16629.

Regards,

Federico Miyara


On 10/01/2021 11:18, Samuel Gougeon wrote:
> Le 10/01/2021 à 08:18, Federico Miyara a écrit :
>>
>> Dear All,
>>
>> I find that the extrapolation option for interp1 is not thoroughly 
>> documented. In the Arguments section it states, for extrapolation,
>>
>>     (optional) string, or real value defining the yp(j) components
>>     for xp(j) values outside [x1,xn] interval.
>>
>>
>> In the Description section the only string listed is "extrap" which says:
>>
>>     the extrapolation is performed by the defined method
>>
>>
>> But which is the defined method? 
>
> <method>, used for interpolation.
>
>
>> If one selects the method "spline" it is suggested to refer to 
>> interp(), which has a specific argument (called out_mode) with 
>> several possibilities for extrapolation. These possibilities aren't 
>> accessible from the interp1() function, so it should be completely 
>> clear in its documantation which one is used.
>
>
> Right. This is true also for interp(), for which the default 
> extrapolation behavior is not documented.
>
>
>>
>> Besides, the argument extrapolation is optional but it is not clear 
>> what happens if it is not used. I suppose it is what appears under 
>> "by default",
>
>
> Sure
>
>
>> but again it says
>>
>>     the extrapolation is performed by the defined method (for spline
>>     method)
>>
>>
>> But, as already mentioned, tha spline method has more than one 
>> extrapolation strategy, which can be selected from interp but not 
>> from interp1.
>
>
> It is the same remark as above.
>
>> Finally, at least for spline it seems to be no difference between 
>> setting the extrapolation argument to "extrap" or not using it.
>
> According to the current documentation,
>
> interp1(x, y, xp, "spline", "extrap")  // is equivalent to
> interp1(x, y, xp, "spline", "spline")
>
> // while
>
> interp1(x, y, xp, "spline")  // is as well equivalent to
> interp1(x, y, xp, "spline", "spline")
>
> So yes, same results are expected.
>
> But i find as well the "by default" explanation uselessly complicated: 
> From
> /  by default ://
> //       the extrapolation is performed by the defined method (for 
> spline method), and by nan for//
> //       linear and nearest methods. yp=interp1(x,y,xp,method)//
> /it could rather be something like
> /  by default ://
> //       the extrapolation is performed by spline when the 
> interpolation is done by spline, and by nan for//
> //       linear and nearest interpolation methods.//
>
> /Samuel Gougeon
>
> /
> /
>
>
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