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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