Holding parameters constant

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:

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:

**Table 4.8:** Hotkeys to hold, free and set parameters.
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