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Info/Interpolate Problem

 
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marquiz



Joined: 15 Feb 2006
Posts: 3

PostPosted: Wed Feb 15, 2006 10:00 am    Post subject: Info/Interpolate Problem Reply with quote

I've been interpolating data off of 7 curves on a Linear X, Log Y plot. X values are dates ranging from 6/25/1958 to 5/5/2005. The X values I've entered for interpolation have been the 15th of each month. Info/Interpolate has returned Y values up to X = 5/15/1990. At X = 6/15/1990, clicking on the OK button causes DPlot to automatically close. I don't know if this is a quirk in DPlot or a problem with some settings, ie array size. Any help is appreciated.
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DPlotAdmin
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Joined: 24 Jun 2003
Posts: 2291
Location: Vicksburg, Mississippi

PostPosted: Wed Feb 15, 2006 3:15 pm    Post subject: Reply with quote

Off the top of my head I'd guess there's an integer overflow problem that can be fixed by rearranging things a bit. It would be helpful to me if you'd send me an example file that you have this problem with.
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David Hyde
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marquiz



Joined: 15 Feb 2006
Posts: 3

PostPosted: Wed Feb 15, 2006 4:15 pm    Post subject: Info/Interpolate Problem .grf File emailed Reply with quote

I emailed (@ 3:10 p.m.) the DPlot .grf file that I have been working with.

Let me know if you need anything else.
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DPlotAdmin
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PostPosted: Wed Feb 15, 2006 4:41 pm    Post subject: Reply with quote

Mark,
File received, thanks. The problem is with your Well #2. The points bounding 6/15/1990 are 5/15/1990 and 5/15/1994. Both points have a 0 amplitude. DPlot is using logarithms to interpolate on your log(Y) scale and crashing as a result of taking log(0). (As an aside, it wasn't too many versions ago that DPlot would have refused to allow a log Y scale in this case. In the past several versions your data is accepted, but those points aren't plotted.) I just need to add a check for 0 values here; should have it ready late tonight. Sorry for the trouble.
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marquiz



Joined: 15 Feb 2006
Posts: 3

PostPosted: Wed Feb 15, 2006 5:30 pm    Post subject: Reply with quote

Thanks for the replies!

For purposes of interpolation, would it it be better to just use a Linear X Linear Y plot? I thought I read an earlier thread or FAQ where you mentioned a difference in accuracy due to interpolation methods used. I can replot my data and interplot a few points to see if the difference is significant enough.
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DPlotAdmin
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PostPosted: Wed Feb 15, 2006 5:47 pm    Post subject: Reply with quote

Mark,
It all depends on what you're trying to do and what the real relationship is between your X and Y. Take a look at the description of the Interpolate command in the Help file (search for Interpolate) to see an example of the difference you might get. In general, if your points are spaced far apart then you'll get a large difference between linear and logarithmic interpolation.

Another example: say you have a linear X-log Y scale with 2 points at 0,1 and 2,100. Interpolating at X=1 on this scale will give Y=10. With a linear X, linear Y scale you'll get Y=50.5. Which is correct? Well... it depends. If there's really a logarithmic relationship between X and Y (in this case, something like Y=10^X) then you're better off using that interpolation. But if you're only using a log Y scale as a matter of convenience then the linear interpolation is probably more appropriate.

Hope this helps.
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DPlotAdmin
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PostPosted: Wed Feb 15, 2006 6:48 pm    Post subject: Reply with quote

Fixed. For 0 values on a log scale (X or Y) at either point bounding the X value of interest, the interpolation scheme now uses linear interpolation. Licensed users can get the update with Help>Check for Updates.

Recent changes:

DPlot v2.0.3.5
Feb-15-2006

  • Edit>Edit Data now allows you to click on the plot to edit the currently selected point or add a new point. If the point specified with the mouse is the last point in the set, a new point is added. (Needs a bit of work yet. If adding data points using the mouse you'll always end up with an extra 0,0 that you'll most likely want to delete.)

  • Bug fix: Info>Interpolate might have crashed if a log scale was used and the data being interpolated contained 0 values on the log axis.



DPlot v2.0.3.4
Feb-14-2006


  • When panning a zoomed plot, pressing the Ctrl key in combination with the arrow keys now pans the plot by 10% of the normal pan distance. (By default, the pan distance is one half of the plot extents. This fraction can be reset with a SetPanFraction macro command.)

  • If the crosshair cursor is used, that cursor is now used during a Distance Between Points command. In previous versions the cursor reverted to the default arrow when any dialog box was opened.

  • Point labels for invisible curves are not drawn.

  • The Colors dialog for XY plots now includes curve legends in the label rather than the generic Curve 1, Curve 2, etc.

  • Improved the new N1.85 scaling option a bit. Previous version did not allow X values equal to 0. This was simply to avoid math errors and not a physical limitation of the scale.

  • Bug fix: DPlot crashed due to an integer overflow if you selected a tick mark interval smaller than either extent divided by about 2 billion (more precisely, 0x7FFFFFFF). This would commonly be a problem when working with calendar dates and a tick mark interval of 1 second or smaller.

  • Bug fix: The default extents on XY plots often cut off portions of the data, if the magnitude of the X or Y values was much larger than the default tick mark interval

  • Bug fix: Edit>Edit Data did not use a sufficient number of significant figures in some cases.

  • Bug fix: Edit>Copy Data Values did not use a sufficient number of significant figures for XY plots with date/time groups on the X axis.


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