Finding Zeros in 3D Data Set with GSL

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Discussion Overview

The discussion revolves around finding zeros in a 3D data set using root-finding methods, specifically with the GNU Scientific Library (GSL). Participants explore various approaches to determine where the function defined by the data set equals zero, considering interpolation methods and assumptions about the data.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant inquires about root-finding methods for a 3D data set where z = f(x,y) and expresses a preference for using GSL.
  • Another participant suggests searching for values of z that are exactly zero or identifying sign changes between consecutive z values as potential methods.
  • A different participant emphasizes the need for interpolation to locate the exact points where the function equals zero, indicating a desire for more precision than simple sign change detection.
  • One participant notes that the choice of method may depend on the assumptions made about the data and mentions various fitting techniques, including linear, quadratic, and cubic fits.
  • A participant shares a resource on using GSL for interpolation, providing a link to a relevant page.

Areas of Agreement / Disagreement

Participants express differing views on the best approach to find zeros, with some advocating for interpolation methods while others suggest simpler techniques. There is no consensus on a single method, and the discussion remains unresolved.

Contextual Notes

The discussion highlights the dependence on assumptions about the data and the various fitting methods available, but does not resolve the specifics of the mathematical steps involved in the proposed approaches.

r4nd0m
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Hi,
does anyone know of some nice root-finding method (preferable GSL :-)) for a data set - i.e. I have a set of 3D data (x,y,z) where z = f(x,y,) and I want to know where the zeros of f are. I guess, I could write it myself with some interpolation method, but just in case someone knows...
 
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If you have the function only in terms of triples, then the best you can do is search for:
1. Values of z which are actually equal to zero.
2. Sign changes from one value of z to the next.
 
yeah, but I'd like to know where exactly the points are, so the method I'm searching for should be using some kind of interpolation and then find the zeros.
 
Ah. Well this depends on the assumptions you make about the data. You could do a linear (or quadratic, or cubic, or some other polynomial) local fit/spline, or you could choose any of a number of other types of fits.

There's a free ("as in beer") program out there called CurveExpert that does this reasonably well, if you'd like to try it.
 

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