Re: fitting arbitrary nth degree polynomial?

Posted by Wayne Rasband on Jan 05, 2009; 9:50pm
URL: http://imagej.273.s1.nabble.com/fitting-arbitrary-nth-degree-polynomial-tp3694105p3694107.html

On Jan 5, 2009, at 3:35 PM, Bill Christens-Barry wrote:

> Does anyone know of a plugin that would allow me to fit a parabola, or
> more generally an arbitrary
> nth-degree polynomial (up to whatever n is currently supported), to
> (x, y) coordinate pairs? This
> would amount to constraining the coefficients of some terms to equal 0.

You can use the curve fitter built into ImageJ. Here is an example
macro that fits a 3rd degree polynomial to 25 data points.

   n = 25;
   xpoints = newArray(n);
   ypoints = newArray(n);
   xmin = -2;
   xmax = 2;
   xinc = (xmax-xmin)/(n-1);
   x = xmin;
   for (i=0; i<n; i++) {
       xpoints[i] = x+random/6;
       ypoints[i] = x*x+random/6;
       x += xinc;
   }
   Fit.doFit("3rd Degree Polynomial", xpoints, ypoints)
   Fit.plot

Look at the source for the plugin that implements the
Analyze>Tools>Curve Fitting command for an example of how to do curve
fitting in a plugin.

      http://rsb.info.nih.gov/ij/source/ij/plugin/frame/Fitter.java

-wayne