reading between the lines?

[Daddio]

I regularly plot x-y graphs of a spring's force vs
height. Height is X; force is Y. This data is acquired
somewhat arbitrarily--I never really know what exact x
values will end up in my table. So when I want to compare
two springs at any specific height, I have to either
guesstimate based on the chart or find values that match
close enough. I have also written specific FORECAST
functions to find the comparison points between two real
data points. But geez that takes too long!
How can I take multiple x-y tables with any ol' values in
x, and (what's the word?) normalize them to have the same
x values? (Clear as mud?)

 

[Jerry W. Lewis]

Excel's chart smoother appears to use Bezier curves.
Brian Murphy has posted code for Bezier curves.

http://www.xlrotor.com/excel_stuff.htm

In most cases, the difference between Bezier curves and cubic splines is
minimal. An example where the difference is noticeable is

http://www.google.com/groups?threadm=3E7291CA.7020907@no_e-mail.com

David Braden has posted code for cubic splines

http://www.google.com/[email protected]

It sounds like your functions are monotonic.
http://groups.google.com/groups?selm=3BB60A1E.7020709@no_e-mail.com
mentions an approach for mononotonic interpolation that might work for you.

Jerry

 

[Bernard Liengme]

Do your springs obey Hooke's Law?
Bernard