software to fit optical spectra - Quantum Materials Group

At each iteration a linear equation system with the α -matrix is solved (Equation 2-9). It
becomes impossible when the determinant of the matrix is getting too small. This happens, for
instance, if one of the active parameters does not affect the value of chi-square. In this case the
iterations stop. One can specify the minimal allowed value of the determinant, which is by
default 10 -30 .
The initial value of λ can also be modified (the default value is 0.001).
4.10.3. Starting/stopping fitting process
To start the automated fitting one should click the button (Figure 4-19). Only a
very limited set of actions is allowed when the fit is running (e.g., one can resize the windows).
The process can be stopped by the same button, which is now looks as . It may take some
time before the program really stops, because it must complete the current iteration.
During the fitting process the following quantities are displayed: the current value of this
chi-square, its absolute change compared to the initial value, the number of iterations and
elapsed fitting time.
In order to recover the previous parameter values before the last fitting started, one
should click the buttons 22 . It is only possible right after the fitting run.
4.11. Macro language
Once you have found a good data fit, you may need to do the same task many times, for
instance, to fit the same kind of spectra for different temperatures. Each case, however,
involves an appreciable number of actions, such as opening a model, loading data, adding chisquare
terms and so forth. Imagine, how many mouse clicks have to be done to fit spectra for,
let’s say, 10 temperatures! And what about 300 temperatures?!!!
To facilitate the execution of routine operation the macro scripts are indispensable.
Another advantage of scripts is the possibility to modify them in order to tackle new problems,
which are similar to the ones already solved. Also, a script may serve as a sort of logbook,
which helps to recollect, how exactly a particular data analysis has been performed a long time
ago.
4.11.1. Writing and executing macros
Macro scripts are stored as text files, which can be created and modified using any text
editor such as Windows Notepad. Make sure, that the file is saved as a usual, or ANSI, text
(and not, for example, as UNICODE text). The convention is (although it is not obligatory) to
use the extension ‘RFS’ to macro files, for instance “MACRO1.RFS”.
Once a macro is created, it can be executed at the stage when RefFIT starts. One should
call the RefFIT program supplemented with the macro file name, for example
“D:\REFFIT\REFFIT.EXE MACRO1.RFS”. In this case the executable file “REFFIT.EXE”
21 The screen update time is usually only a minor fraction of the total computing activity.
22 this option is not realized yet
Guide to RefFIT Page 79