[Scilab-users] Insufficient documentation of interp1

[Federico Miyara]

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? 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.

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", 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.

Finally, at least for spline it seems to be no difference between 
setting the extrapolation argument to "extrap" or not using it.

Regards,

Federico Miyara


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