Fitting system of equation
Danny Vandam
I am a low-level user of Igor; despite reading a lot of threads in the forum I was unable to find a solution for my problem so I will be very happy to get some advices.
Here is my issue; I have a set of experimental data, u, v, w, to fit in function of one variable, R, the same process characterizing their relationship, thanks to three parameters. So, a global fitting will do the job easily, having three functions for u(R), v(R) and w(R)... unfortunatelly, impossible as linear relationship are implied...
The best I can do is to express two of them in function of the variable and the last one, so w = fct(R, v) and u = fct(R, v). The last equation of the system allows me to obtain an non linear expression fct(R,v) = 0, for wich I can use Findroots to obtain v values during the fitting process for either u or w. I would thus be able to perform a global fitting on both u and w. But I cannot use the experimental v values I have to obtain a better fit...
My questions are thus (i) is there a better way to fit a system of equation? (ii) if not, how is it possible to extract the roots (v) used during the fitting process?
Thanks for help
suggests that you might be able to use implicit fitting:
DisplayHelpTopic "Fitting Implicit Functions"
To understand that section, you really need to start with the previous section:
DisplayHelpTopic "Errors in Variables: Orthogonal Distance Regression"
Copy those commands, paste them into Igor's command line, and press Enter.
John Weeks
WaveMetrics, Inc.
support@wavemetrics.com
April 6, 2015 at 10:13 am - Permalink