The constraints which are placed on the fitting procedure and individual peaks must be specified in a separate ASCII file with the *.cst extension. The constraints section of the file must begin with:

****_Constraints_File_Begins_****

and end with:

****_Constraints_File_Ends_****

The constraints file contains three distinct sections called:

[Parameters]

[Variables]

[Peaks]

Each section contains specific information which is interpreted by the fitting routine.

The [Parameters] sections contains the following:

The [Variables] section contains the following:

<s>  <n>

where <s> specifies the variable name and <n> specifies the value assigned to it.

The [Peaks] section contains the following:

;PEAK#  SHIFT     LORENTZIAN WIDTH    AMPLITUDE    PHASE    DELAY     GAUSSIAN WIDTH
1       {shift1} {lorentzian_width1} {amplitude1} {phase1} {delay1} {Gaussian_width1}

repeated for every peak.

The semi-colon identifies a remark and forces the parsing routine to ignore this line.

The strings within the curly brackets identify the variable name used for linking. Therefore any other peak can be linked to the above peak parameters by specifying the same string. Offsets can also be used for linking. For example the second peak and third peaks could be constrained as follows:

2   {shift2} {lorentzian_width2} {amplitude1}*2 {phase1} {delay1} {Gaussian_width2}
3   {shift3} {lorentzian_width3} {amplitude1}   {phase1} {delay1} {Gaussian_width3}

This is interpreted as follows. Since each peak has a different string to constrain SHIFT these will be fit as independent parameters. The same is true for LORENTZIAN WIDTH and GAUSSIAN WIDTH parameters. The amplitude strings for all three peaks are the same, although the amplitude for peak two is scaled by a factor of 2. Therefore this identifies a triplet with the amplitude ratios 1:2:1. Similarly, since the PHASE and DELAY strings are the same for all three peaks, they are all linked. Since no offsets are provided for these parameters, they will all have the same value.

When linking parameters the following functions can be used:

Multiple arguments can also be use as long as no spaces separate them. For example:

{shift1}+-0.5+0.1

This will be resolved to {shift1}-0.4.

Any peak parameter can be fixed to the value specified for the corresponding peak in the guess file by placing an @ sign in front of the first curly bracket of the parameter constraint. For example:

4   @{shift3} @{lorentzian_width3} @{amplitude1} @{phase1} @{delay1} @{Gaussian_width3}

This fixed the value of each parameter to the corresponding guess in the guess file. It makes no difference what the strings are within the curly brackets (these are ignored).

Limits may also be specified for specific parameters using the > or < symbols. This ensures that parameters will not exceed the specified values in the fitting. If a limit is exceeded, the parameter is removed from the fit and the entire fit is restarted using the current set of parameter values as the initial guess. A message to this effect is given during the fit (i.e. peak 1 parameter 3 has exceeded minimum bounds). Parameters are removed from the fit according to the following rules:

4   @{shift3} @{lorentzian_width3} {amplitude1} >0 @{phase1} @{delay1} @{Gaussian_width3}