Definition of a fit

It is possible tell GICO to change certain parameters of the system to minimize a variable. GICO needs to know the variables that are to be changed, and the locations in which the variables appear. The command which starts a fit is: 2 F(IT) B(EGIN) <list of variables> ; [example: F   B   A   B   C ;]

The list can consist of up to 10 variables. The variables have to be defined prior to the F B command. There are a few restrctions for these variables:

• The variables may appear only in one fit. Use different variables for different fits.
• The variables must not be used as parameters of commands prior to the fit.
• Do not change the values of these variables with assignment statements after the fit.

Following the F B command are GICO commands, in which the fit variables have to appear. At the position where the variables that are to be fitted can be computed, the command: 2 F(IT) V(ARIABLES) <list of fit variables> ; [example: F   V   F1   F2 ;]

must be inserted. Note that there is a difference between naming only one or several variables; in each case, different routines are used internally.
The command: 3 F(IT) E(ND)<tolerance> <max. Iterations> <fit routine> ; [example: F   E   1.E-5   150   1 ;] [default: F   E   1.E-4   100   1 ;]

ends the fit. The value for the fit routine for a single fit variable may be between 1 and 6. If more than one variable is to be fitted, the value of the fit routine must be 1, which is the default. GICO tries to change the variables in a way that the fit variables become 0. The success of the fit depends on the chosen fit variable, the fit routine, the tolerance and the starting values for the variables. The results of the fit can be looked up in the GICO output. They are also written in a more compact form onto the file GICOFIT.DAT.
Sometimes it may be desirable to disable a fit for one calculation. This can be done by commenting out the Fit Begin, Fit Variables and Fit End commands. A quicker way is to use the command: 2 F(IT) D(ISABLE)  ; [example: F   D ;]

which may appear between a Fit Begin and Fit End and will prevent this fit from being executed.