Parameter control / priors
The code now offers several ways to impose explicit constraints
on parameters or relations between parameters. These can be
thought of as a type of prior.
pbounds
Lets you specify fixed ranges for model parameters. The
parameter is completely free within the allowed range, but
forbidden from going outside that range. The constraint file
has the following form:
#constraints
igal ip lo hi
...
Sequential calls load additional constraints.
plimits
Lets you impose a prior that a given parameter should have a
certain value, within some uncertainty. The form of the constraint
file is:
#constraints
igal ip value sigma
...
In practice, this adds an addition term to the chisq of the form
(model - value)2 / sigma2
As before, sequential calls load additional constraints.
pmatch
Lets you specify relations between parameters. The form
of the constraint file is:
#constraints
igal ip jgal ip ratio sigma
...
For each constraint with sigma = 0, the code forces the exact
relation
p[igal][ip] = ratio * p[jgal][jp]
For each constraint with sigma != 0, the code adds a chisq term
of the form
( p[igal][ip] - ratio*p[jgal][jp] )2 / sigma2
And as always, sequential calls load additional constraints.