# Component/ parameter constraint Comment
# operation (see below) range
3 n 0.7 to 5 # Soft constraint: Constrains the
# sersic index n to within
# ABSOLUTE values from 0.7 to 5.
2 x -1 0.5 # Soft constraint: Constrains
# x-position of component
# 2 to within +0.5 and -1 of the
# INPUT value.
2 x -1 in 0.5 # Alternative version of above.
1 x -2.0 ref 2.0 # Soft constraint: Constrains
# x-position of component
# 1 to within +2.0 and -2.0 of the
# value at the REFERENCE wavelength.
1 re factor 3.0 # Soft constraint: Constrains the
# Re to be within a factor of 3 of the
# input value (new in GALFITM)
3 n_1 -10 to 10 # Soft constraint: Constrains the first
# order (linear) Chebyshev coefficient
# describing the dependence of component
# three's sersic index n on wavelength
# to within values from -10 to 10.
2 re_B -1 0.5 # Soft constraint: Constrains the B-band
# effective radius of component two to be
# within +0.5 and -1 of the input value.
3-7 mag -0.5 3 # Soft coupling-constraint: The magnitude
# of component 7 is constrained to
# be WITHIN a range -0.5 mag brighter
# than component 3, 3 magnitudes
# fainter.
3/5 re 1 3 # Soft constraint: Couples components
# 3 and 5 Re or Rs ratio to be greater
# than 1, but less than 3.
3_2_1_9 mag offset # Hard coupling-constraint: Constrains
# the magnitude of components 3, 2,
# 1, and 9 to maintain RELATIVE offsets as
# defined by the initial parameter file,
# provided no wavelength dependence of x
# is allowed.
1_5_3_2 re ratio # Hard coupling-constraint: similar to above
# except constrain the Re parameters
# by their ratio, as defined by the
# initial parameter file, provided no
# wavelength dependence of x is allowed.
1_2_3 x_0 offset # Hard coupling-constraint: The x-position
1_2_3 x_1 offset # of components 1, 2 and 3 are constrained
1_2_3 x_2 offset # to maintain their initial offsets, in the
# case where a quadratic dependence on
# wavelength is permitted.
# Note on parameter column:
# The parameter name options are x, y, mag, re (or rs -- it doesn't matter),
# n, alpha, beta, gamma, pa, q, c, f1a (Fourier amplitude), f1p (Fourier
# phase angle), f2a, f2p, r5 (coordinate rotation), etc., . Or
# alternatively, one can specify the parameter number instead (for the
# classical parameters only) corresponding to the same numbers in the
# galfit input file.
# Notes for multi-band data:
# The format for specifying constraints in GALFITM is essentially the
# same as for GALFIT3, with a few additions and caveats, as described
# below.
# Note that the way in which constraints are applied has changed in
# GALFITM, so single-band fits with GALFITM will sometimes give
# different results to GALFIT3. As there are hard-coded constraints
# (e.g. re > 0), differences can occur even without user-specified
# constraints.
# Constraints are applied in order. However (to avoid potential
# confusion) hard coupled-component constraints are always applied
# last.
# Fourier and rotational transforms are not supported with multi-band data.
#
# Soft single-component constraints:
# These constrain a single parameter to lie between two limiting
# values. Unadorned parameter names imply constraints which apply
# across all the input wavelength bands. However, if desired, these
# constraints can be applied to specific bands or Chebyshev
# coefficients (see below).
# For convenience, GALFIM introduces an option for constraining a
# parameter value to be within some factor of the input value.
# Soft coupled-components constraints:
# These can only be specified in terms of Chebyshev coefficients
# (see below), and not in terms of actual band values. Enabling
# this for band values should be possible, but remains to be
# implemented. Unadorned parameter names imply constraints which
# affect only the zeroth-order Chebyshev coefficient (i.e. the
# constant value with wavelength). They are therefore useful, and
# behave as expected, if you are not allowing any wavelength
# dependence in the parameter in question. Any other use of
# soft-coupled constraints (i.e. for parameters with non-constant
# wavelength dependence) is inadvisable.
# Hard coupled-components constraints:
# These can only be specified in terms of Chebyshev coefficients,
# (see below). It is not possible to implement hard-coupling in
# terms of the actual band values. Unadorned parameter names imply
# constraints which affect only the zeroth-order Chebyshev
# coefficient (i.e. the constant value with wavelength). They are
# therefore useful, and behave as expected, if you are not allowing
# any wavelength dependence in the parameter in question. If you
# are allowing the parameters more freedom to vary with wavelength,
# and you wish them to be fully-coupled then you must specify
# constraints for all the free Chebyshev coefficients individually.
# Hard coupling some, but not all, Chebyshev coefficients for a
# parameter is inadvisable.
# Individual band values:
# If you wish to apply a constraint to a specific band, the usual
# parameter names may be appended with "_bandlabel", where bandlabel
# is the label of the band in question, as specified in parameter A1
# of the GALFITM input file. One may also append "_all" to
# explicitly indicate all bands.
# Cheybshev coefficient values:
# If you wish to constrain specific Chebyshev coefficients, the
# usual parameter names may be appended with "_i", where i
# indicates the Chebyshev coefficient (i=0...nbands)