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List:       gnuplot-info-beta
Subject:    Re: glitch in cosine
From:       Ethan Merritt <eamerritt () gmail ! com>
Date:       2013-10-21 19:20:27
Message-ID: CAGRdh4vsvqn1KrTfXLSqusX+0E-E6pxy3riyBZJqHDY4xt9Ffg () mail ! gmail ! com
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As Hans-Bernhard points out,  "set samples" has no effect on the data file.

The point is that the function f3(x) has a period of ~1 along x in the
coordinate system of the data file (see attached graph).

The data itself has a sampling interval of ~7.  So plotting at those
intervals is sampling too coarsely by a factor of ~1000 to see the true
underlying curve f3(x).   The plot of the data cannot be corrected by
changing "set sample", but a separate plot of f3(x) can be, and does show
that the value of f3 at that "glitch" point may be corrrect.



On Mon, Oct 21, 2013 at 6:57 AM, Hans-Bernhard Br=C3=B6ker <HBBroeker@t-onl=
ine.de
> wrote:

> On 21.10.2013 02:40, sfeam wrote:
>
>> I suspect that despite your large value for "set sample"
>> you are still sampling too coarsely by a factor of a thousand or so.
>> The smooth curve you see is probably an aliasing artifact.
>>
>
> The setting of "set samples" has no effect on this plot, because the plot
> is made from data:
>
>
>         plot  datafile u (($1)/365.25+1945):(f3($1)) w l
>
> But neither the current CVS version nor 4.6.2 shows the problem here.
> The reason for that may very well be that the subset of the data presente=
d
> to us is missing one data point (at 22671, transformed x value 2007.07),
> which might be just where that "peak" is.
>

[Attachment #5 (text/html)]

<div dir="ltr">As Hans-Bernhard points out,   &quot;set samples&quot; has no effect \
on the data file.<div><br><div>The point is that the function f3(x) has a period of \
~1 along x in the coordinate system of the data file (see attached graph).</div> \
<div><br></div><div>The data itself has a sampling interval of ~7.   So plotting at \
those intervals is sampling too coarsely by a factor of ~1000 to see the true \
underlying curve f3(x).    The plot of the data cannot be corrected by changing \
&quot;set sample&quot;, but a separate plot of f3(x) can be, and does show that the \
value of f3 at that &quot;glitch&quot; point may be corrrect.   </div> \
<div><br></div></div></div><div class="gmail_extra"><br><br><div \
class="gmail_quote">On Mon, Oct 21, 2013 at 6:57 AM, Hans-Bernhard Bröker <span \
dir="ltr">&lt;<a href="mailto:HBBroeker@t-online.de" \
target="_blank">HBBroeker@t-online.de</a>&gt;</span> wrote:<br> <blockquote \
class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc \
solid;padding-left:1ex"><div class="im">On 21.10.2013 02:40, sfeam wrote:<br> \
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc \
solid;padding-left:1ex"> I suspect that despite your large value for &quot;set \
sample&quot;<br> you are still sampling too coarsely by a factor of a thousand or \
so.<br> The smooth curve you see is probably an aliasing artifact.<br>
</blockquote>
<br></div>
The setting of &quot;set samples&quot; has no effect on this plot, because the plot \
is made from data:<div class="im"><br> <br>
            plot   datafile u (($1)/365.25+1945):(f3($1)) w l<br>
<br></div>
But neither the current CVS version nor 4.6.2 shows the problem here.<br>
The reason for that may very well be that the subset of the data presented to us is \
missing one data point (at 22671, transformed x value 2007.07), which might be just \
where that &quot;peak&quot; is.<br> </blockquote></div><br></div>

--047d7bdc90ec3f7b2404e9452d1d--


["f3.png" (image/png)]

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