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smoothed line on chart -> problems


Posted by Pasi Vartiainen on August 29, 2001 3:11 AM

This might have been asked previously, but your archive is HUGE, so...

I'm having chart where values sometimes are = 0, but never below. ( All values are squared )

When smooth line option is on from Format Data Series dialog, line goes visibly below zero, which isn't possible.

Does someone have suggestion what to do?

- pasi -


Posted by Mark w. on August 29, 2001 7:22 AM

I can't reproduce your problem. -- provide sample data. (NT)

Posted by Eric on August 29, 2001 11:24 AM

Splines and beziers

I think it is possible for a spline fit (the smoothed line option) to generate values below 0, and, for that matter, above some maximum limit.

In fact, if you open the graph wizard and select the scatter plot option, you'll see a group of graph types for X-Y graphs. One of these is a smoothed line graph, and even in their example, the smoothed line dips below the minimum value of the data to which it is fit.

I've got a call in to a math friend of mine who specializes in this sort of work, I'll let you know what he says- if I can figure out what he's saying!

Posted by Eric on August 30, 2001 12:09 PM

Splines and Tigers and Beziers, oh my!

This is the message I got back from Dr. Alfeld regarding splined/smoothed data falling outside the raw data to which it was fit.

"Eric,

That depends on the precise scheme that's being used. For many, if not
most, schemes the extreme values of the interpolant and approximant
will be outside the range determined by the extreme values of the
data.

Sincerely,

Peter Alfeld"