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List: scilab-users
Subject: Re: [Scilab-users] Insufficient documentation of interp1
From: Federico Miyara <fmiyara () fceia ! unr ! edu ! ar>
Date: 2021-01-11 4:36:44
Message-ID: 32b31e87-810a-aed5-3377-6426e6f082af () fceia ! unr ! edu ! ar
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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
>
> /
> /
>
>
> _______________________________________________
> users mailing list
> users@lists.scilab.org
> http://lists.scilab.org/mailman/listinfo/users
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<br>
<font face="Courier New">Samuel,<br>
<br>
Thanks for your comments, which encouraged me to submit bug
#16629.<br>
<br>
Regards,<br>
<br>
Federico Miyara<br>
<br>
</font><br>
<div class="moz-cite-prefix">On 10/01/2021 11:18, Samuel Gougeon
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:4e956401-9804-17d4-91de-86c001d58e7f@free.fr">
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<div class="moz-cite-prefix">Le 10/01/2021 à 08:18, Federico
Miyara a écrit :<br>
</div>
<blockquote type="cite"
cite="mid:ddea38be-bd32-53e9-b5d9-2fd670ce1cc5@fceia.unr.edu.ar">
<meta http-equiv="content-type" content="text/html;
charset=UTF-8">
<br>
<font face="Courier New">Dear All,<br>
<br>
I find that the extrapolation option for interp1 is not
thoroughly documented. In the Arguments section it states, for
extrapolation,</font><br>
<br>
<blockquote>(optional) string, or real value defining the yp(j)
components for xp(j) values outside [x1,xn] interval.<br>
</blockquote>
<br>
In the Description section the only string listed is "extrap"
which says:<br>
<br>
<div class="refsection">
<dl>
<dd>
<p class="para"> the extrapolation is performed by the
defined method </p>
</dd>
</dl>
</div>
<font face="Courier New"><br>
But which is the defined method? </font></blockquote>
<p><font face="Courier New"><method>, used for
interpolation.</font></p>
<p><font face="Courier New"><br>
</font></p>
<blockquote type="cite"
cite="mid:ddea38be-bd32-53e9-b5d9-2fd670ce1cc5@fceia.unr.edu.ar"><font
face="Courier New">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.<br>
</font></blockquote>
<p><br>
</p>
<p><font face="Courier New">Right. This is true also for interp(),
for which the default extrapolation behavior is not
documented.<br>
</font></p>
<p><br>
</p>
<blockquote type="cite"
cite="mid:ddea38be-bd32-53e9-b5d9-2fd670ce1cc5@fceia.unr.edu.ar"><font
face="Courier New"> <br>
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",</font></blockquote>
<p><br>
</p>
<p><font face="Courier New">Sure</font></p>
<p><br>
</p>
<blockquote type="cite"
cite="mid:ddea38be-bd32-53e9-b5d9-2fd670ce1cc5@fceia.unr.edu.ar"><font
face="Courier New"> but again it says<br>
<br>
</font><font face="Courier New"> </font>
<div class="refsection">
<dl>
<dd>
<p class="para"> the extrapolation is performed by the
defined method (for spline method) </p>
</dd>
</dl>
</div>
<br>
But, as already mentioned, tha spline method has <font
face="Courier New">more than one extrapolation strategy, which
can be selected from interp but not from interp1.<br>
</font></blockquote>
<p><br>
</p>
<p><font face="Courier New">It is the same remark as above.<br>
</font><br>
</p>
<blockquote type="cite"
cite="mid:ddea38be-bd32-53e9-b5d9-2fd670ce1cc5@fceia.unr.edu.ar"><font
face="Courier New"> Finally, at least for spline it seems to
be no difference between setting the extrapolation argument to
"extrap" or not using it.<br>
</font></blockquote>
<p>According to the current documentation,</p>
<p><font size="+1" face="monospace">interp1(x, y, xp, "spline",
"extrap") // is equivalent to<br>
interp1(x, y, xp, "spline", "spline")<br>
</font><br>
// while<br>
<font size="+1"><br>
interp1(x, y, xp, "spline") // is as well equivalent to<br>
interp1(x, y, xp, "spline", "spline")<br>
</font></p>
<p>So yes, same results are expected.<br>
</p>
<p>But i find as well the "by default" explanation uselessly
complicated: From<br>
<i> by default :</i><i><br>
</i><i> the extrapolation is performed by the defined
method (for spline method), and by nan for</i><i><br>
</i><i> linear and nearest methods.
yp=interp1(x,y,xp,method)</i><i><br>
</i>it could rather be something like<br>
<i> by default :</i><i><br>
</i><i> the extrapolation is performed by spline when the
interpolation is done by spline, and by nan for</i><i><br>
</i><i> linear and nearest interpolation methods.</i><i><br>
<br>
</i>Samuel Gougeon<br>
</p>
<p><i><br>
</i></p>
<br>
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