The default Command

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1.4.5.2 The default Command

Each task has a special set of default parameters defined for its parameters. You can use the default command to reset the parameters for a specified task (or the current task as defined by the taskname variable) to their default.

Important Note: The default command resets the values of the task parameters to a set of “defaults” as specified in the task code. Some defaults are blank strings ’’ or empty lists [], others are specific numerical values, strings, or lists. It is important to understand that just setting a string parameter to an empty string ’’ is not setting it to its default! Some parameters do not have a blank as an allowed value. See the help for a particular task to find out its default. If ’’ is the default or an allowed value, it will say so explicitly.

For example, suppose we have been running CASA on a particular dataset, e.g.

CASA <40>: inp clean
---------> inp(’clean’)
#  clean :: Deconvolve an image with selected algorithm
vis                 = ’ngc5921.demo.src.split.ms.contsub’ #  name of input visibility file
imagename           = ’ngc5921.demo.cleanimg’ #  Pre-name of output images
field               =        ’0’        #  Field Name
spw                 =         ’’        #  Spectral windows:channels: ’’ is all
selectdata          =      False        #  Other data selection parameters
mode                =  ’channel’        #  Type of selection (mfs, channel, velocity, frequency)
     nchan          =         46        #  Number of channels (planes) in output image
     start          =          5        #  first input channel to use
     width          =          1        #  Number of input channels to average
     interpolation  =  ’nearest’        #  Spectral interpolation (nearest, linear, cubic)
niter               =       6000        #  Maximum number of iterations
...

and now we wish to switch to a different one. We can reset the parameter values using default:

CASA <41>: default
---------> default()

CASA <42>: inp
---------> inp()
#  clean :: Deconvolve an image with selected algorithm
vis                 =         ’’        #  name of input visibility file
imagename           =         ’’        #  Pre-name of output images
field               =         ’’        #  Field Name
spw                 =         ’’        #  Spectral windows:channels: ’’ is all
selectdata          =      False        #  Other data selection parameters
mode                =      ’mfs’        #  Type of selection (mfs, channel, velocity, frequency)
niter               =        500        #  Maximum number of iterations
...

It is good practice to use default before running a task if you are unsure what state the CASA global variables are in.

ALERT: You currently can only reset ALL of the parameters for a given task to their defaults. In an upcoming update we will allow the default command to take a second argument with a specific parameter to default its value.

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