Sometimes it is useful to do not fit parameters but keep them constant or in correlation with other parameters. One example is if the energy of one peak in a doublet is known and the other should be fitted, or to set the width of several peaks equal. To do this all steps have to be gone as with the fitting of separated peaks. I.e. set the fit region, background- and peakmarkers and perform the fit.
The short status of the fit (tv fit status short) for two peaks looks as follows:
spectrum #15: ./3_3_11/3_3_11.pry [keV]
#0 pos 716.937(25) wdt 2.298(33) vol 7829(144)
#1 pos 720.160(22) wdt 2.298(33) cor[0] vol 8818(149)
From this one can see that the positions are not held and the widths are correlated, the width of peak1 is set equal to the width of peak0. Now lets set the energy of peak0 to its known value of 717.3 keV and hold this position while the second peak will be fitted. Use the following commands to set and hold the position:
tv fit parameter position0 = 717.3
tv fit parameter position0 hold
The hotkeys to do this are Pp=0 and Pph0. The short status of this fit looks as follows, which shows that position of peak0 is held:
spectrum #15: ./3_3_11/3_3_11.pry [keV]
#0 pos 717.3(0) hol wdt 2.298(33) vol 7829(144)
#1 pos 720.251(22) wdt 2.298(33) cor[0] vol 8818(149)
In the above example the widths of the peaks are correlated. To set correlations the command equal is used and the according command is:
tv fit parameter width1 equal width0
To set all widths free for fitting the following command is used:
tv fit parameter width free
or the hotkey wf respectivelly.
All hotkeys to hold, free and set parameters are given in table 4.8.
Pph0 | tv fit para position0 hold; | Hold position of peak 0. This hotkey is available for peaks 1 to 4 either. |
---|---|---|
Ppf0 | tv fit para position0 free; | The position of peak 0 is set free for fitting. This hotkey is available for peaks 1 to 4 either. |
Ppn0 | tv fit para position0 none; | Peak 0 is removed from the peaklist. This hotkey is available for peaks 1 to 4 either. |
Pp=0 | tv edit; tv fit para position0 = ? | The position of peak 0 is set to the queried value. This hotkey is available for peaks 1 to 4 either. |
Pbh | tv fit param backgr hold; | The background-parameters |
tv fit param exponent hold; | will not be fitted | |
tv fit param factor hold; | ||
Pbf | tv fit param backgr free; | The backfround-parameters |
tv fit param exponent free; | will be fitted | |
tv fit param factor free; | ||
Pwe | tv fit parameter width equal; | The widths of all peaks will be correlated |
HP | tv fit parameter position hold; | The peak position will not be fitted |
HW | tv fit parameter width hold; | The peak width will not be fitted |
we | tv fit parameter width equal; | The widths of all peaks will be correlated |
wf | tv fit parameter width free; | The widths of all peaks will be fitted |