UVCal

UVCal objects hold all of the metadata and data required to work with calibration solutions for interferometric data sets. Calibration solutions are tied to antennas rather than baselines. There are many different kinds of calibration solutions, UVCal has support for many of the most common ones, but this flexibility leads to some complexity in the definition of UVCal objects. The cal_type attribute on UVCal objects indicates whether calibration solutions are “gain” (a complex number per antenna, polarization and frequency) or “delay” (a real number per antenna and polarization) type solutions. The cal_style attribute indicates whether the solution came from a “sky” or “redundant” style of calibration solution. Some metadata items only apply to one cal_type or cal_style.

The antennas are described in two ways: with antenna numbers and antenna names. The antenna numbers should not be confused with indices – they are not required to start at zero or to be contiguous, although it is not uncommon for some telescopes to number them like indices. On UVCal objects, the names and numbers are held in the antenna_names and antenna_numbers attributes respectively. These are arranged in the same order so that an antenna number can be used to identify an antenna name and vice versa. Note that not all the antennas listed in antenna_numbers and antenna_names are guaranteed to have calibration solutions associated with them in the gain_array (or delay_array for delay type solutions). The antenna numbers associated with each calibration solution is held in the ant_array attribute (which has the same length as the gain_array or delay_array along the antenna axis).

For most users, the convenience methods for quick data access (see UVCal: Quick data access) are the easiest way to get data for particular antennas. Those methods take the antenna numbers (i.e. numbers listed in antenna_numbers) as inputs.

UVCal: parameter shape changes

As detailed in UVData: parameter shape changes, UVData objects now support flexible spectral windows and will have several of their parameter shapes change in version 3.0. They also have a method to convert to the planned future array shapes now to support an orderly conversion of code and packages that use UVData objects to the future shapes.

UVCal objects now also support flexible spectral windows and will see parameter shape changes in version 3.0.

Spectral windows are implemented on standard “gain” type UVCal objects in a similar way to the UVData implementation, where windows are defined as sets of frequency channels with some extra parameters to track which channels are in each spectral window. This allows for spectral windows to have arbitrary numbers of frequency channels and makes the channel_width parameter be an array of length Nfreqs rather than a scalar, but only when the UVCal object contains flexible spectral windows. Supporting multiple spectral windows in this way removes the need for the spectral window axis on several UVCal parameters, but the axis was left as a length 1 axis for backwards compatibility.

Spectral windows are treated a little differently for wide-band style UVCal objects, which do not have an explicit frequency axis. For those objects, which include all “delay” type UVCal objects as well as wide-band gain objects, the freq_array and channel_width parameters are not required but the freq_range parameter is required. UVCal objects that are wide-band and use the future array shapes can support multiple spectral windows, see details below.

In version 3.0, several parameters will change shape. For standard “gain” type UVCal objects, the length 1 axis that was originally intended for the spectral windows axis will be removed from the gain_array , flag_array, quality_array, input_flag_array, total_quality_array and freq_array parameters and the channel_width parameter will always be an array of length Nfreqs. For wide-band and “delay” type UVCal objects, the spectral window axis will be retained but the axis corresponding to the frequency axis will be removed from the gain_array , delay_array, flag_array, quality_array, input_flag_array and the total_quality_array and the freq_range parameter will gain a spectral window axis. In addition, the integration_time parameter will always be an array of length Ntimes.

In order to support an orderly conversion of code and packages that use the UVCal object to these new parameter shapes, we have created the pyuvdata.UVCal.use_future_array_shapes() method which will change the parameters listed above to have their future shapes. Users writing new code that uses UVCal objects are encouraged to call that method immediately after creating a UVCal object or reading in data from a file to ensure that the code will be compatible with the forthcoming changes. Developers and maintainers of existing code that uses UVCal objects are encouraged to similarly add that method call and convert their code to use the new shapes at their earliest convenience to ensure future compatibility. The method will be deprecated but not removed in version 3.0 (it will just become a no-op) so that code that calls it will continue to function.

UVCal: Reading/writing

Calibration files using UVCal.

a) Reading a cal fits gain calibration file.

>>> import os
>>> import numpy as np
>>> import matplotlib.pyplot as plt 
>>> from pyuvdata import UVCal
>>> from pyuvdata.data import DATA_PATH
>>> cal = UVCal()
>>> filename = os.path.join(DATA_PATH, 'zen.2457698.40355.xx.gain.calfits')
>>> cal.read_calfits(filename)

>>> # Cal type:
>>> print(cal.cal_type)
gain

>>> # number of calibration jones components and component type.
>>> print((cal.Njones, cal.jones_array))
(1, array([-5]))

>>> # Number of antennas with data
>>> print(cal.Nants_data)
19

>>> # Number of frequencies
>>> print(cal.Nfreqs)
10

>>> # Shape of the gain_array
>>> print(cal.gain_array.shape)
(19, 1, 10, 5, 1)

>>> # plot abs of all gains for first time and first jones component.
>>> for ant in range(cal.Nants_data): 
...    plt.plot(cal.freq_array.flatten(), np.abs(cal.gain_array[ant, 0, :, 0, 0]))
>>> plt.xlabel('Frequency (Hz)') 
>>> plt.ylabel('Abs(gains)') 
>>> plt.show() 

b) FHD cal to cal fits

>>> import os
>>> from pyuvdata import UVCal
>>> from pyuvdata.data import DATA_PATH
>>> obs_testfile = os.path.join(DATA_PATH, 'fhd_cal_data/1061316296_obs.sav')
>>> cal_testfile = os.path.join(DATA_PATH, 'fhd_cal_data/1061316296_cal.sav')
>>> settings_testfile = os.path.join(DATA_PATH, 'fhd_cal_data/1061316296_settings.txt')

>>> fhd_cal = UVCal()
>>> fhd_cal.read_fhd_cal(cal_testfile, obs_testfile, settings_file=settings_testfile)
>>> fhd_cal.write_calfits(os.path.join('.', 'tutorial_cal.fits'), clobber=True)

UVCal: Initializing from a UVData object

The pyuvdata.UVCal.initialize_from_uvdata() method allows you to initialize a UVCal object from the metadata in a UVData object. This is useful for codes that are calculating calibration solutions from UVData objects. There are many optional parameters to allow users to specify additional metadata or changes from the uvdata metadata. By default, this method creats a metadata only UVCal object, but it can optionally create the data-like arrays as well, filled with zeros.

>>> import os
>>> from pyuvdata import UVData, UVCal
>>> from pyuvdata.data import DATA_PATH
>>> uvd_file = os.path.join(DATA_PATH, "zen.2458098.45361.HH.uvh5_downselected")
>>> uvd = UVData.from_file(uvd_file, file_type="uvh5")
>>> uvc = UVCal.initialize_from_uvdata(uvd, "multiply", "redundant")
>>> print(uvc.ant_array)
[ 0  1 11 12 13 23 24 25]

UVCal: Quick data access

Method for quick data access, similar to those on pyuvdata.UVData (UVData: Quick data access), are available for pyuvdata.UVCal. There are three specific methods that will return numpy arrays: pyuvdata.UVCal.get_gains(), pyuvdata.UVCal.get_flags(), and pyuvdata.UVCal.get_quality(). When possible, these methods will return numpy MemoryView objects, which is relatively fast and adds minimal memory overhead.

a) Data for a single antenna and instrumental polarization

>>> import os
>>> import numpy as np
>>> from pyuvdata import UVCal
>>> from pyuvdata.data import DATA_PATH
>>> UVC = UVCal()
>>> filename = os.path.join(DATA_PATH, 'zen.2457555.42443.HH.uvcA.omni.calfits')
>>> UVC.read_calfits(filename)
>>> gain = UVC.get_gains(9, 'Jxx')  # gain for ant=9, pol='Jxx'

>>> # One can equivalently make any of these calls with the input wrapped in a tuple.
>>> gain = UVC.get_gains((9, 'Jxx'))

>>> # If no polarization is fed, then all polarizations are returned
>>> gain = UVC.get_gains(9)

>>> # One can also request flags and quality arrays in a similar manner
>>> flags = UVC.get_flags(9, 'Jxx')
>>> quals = UVC.get_quality(9, 'Jxx')

UVCal: Calibrating UVData

Calibration solutions in a pyuvdata.UVCal object can be applied to a pyuvdata.UVData object using the pyuvdata.utils.uvcalibrate() function.

a) Calibration of UVData by UVCal

>>> # We can calibrate directly using a UVCal object
>>> import os
>>> from pyuvdata import UVData, UVCal, utils
>>> from pyuvdata.data import DATA_PATH
>>> uvd = UVData()
>>> uvd.read(os.path.join(DATA_PATH, "zen.2458098.45361.HH.uvh5_downselected"), file_type="uvh5")
>>> uvc = UVCal()
>>> uvc.read_calfits(os.path.join(DATA_PATH, "zen.2458098.45361.HH.omni.calfits_downselected"))
>>> # this is an old calfits file which has the wrong antenna names, so we need to fix them first.
>>> # fix the antenna names in the uvcal object to match the uvdata object
>>> uvc.antenna_names = np.array(
...     [name.replace("ant", "HH") for name in uvc.antenna_names]
... )
>>> uvd_calibrated = utils.uvcalibrate(uvd, uvc, inplace=False)

>>> # We can also un-calibrate using the same UVCal
>>> uvd_uncalibrated = utils.uvcalibrate(uvd_calibrated, uvc, inplace=False, undo=True)

UVCal: Selecting data

The pyuvdata.UVCal.select() method lets you select specific antennas (by number or name), frequencies (in Hz or by channel number), times or jones components (by number or string) to keep in the object while removing others.

a) Select antennas to keep on UVCal object using the antenna number.

>>> import os
>>> from pyuvdata import UVCal
>>> from pyuvdata.data import DATA_PATH
>>> import numpy as np
>>> cal = UVCal()
>>> filename = os.path.join(DATA_PATH, "zen.2458098.45361.HH.omni.calfits_downselected")
>>> cal.read_calfits(filename)

>>> # print all the antennas numbers with data in the original file
>>> print(cal.ant_array)
[ 0  1 11 12 13 23 24 25]
>>> cal.select(antenna_nums=[1, 13, 25])

>>> # print all the antennas numbers with data after the select
>>> print(cal.ant_array)
[ 1 13 25]

b) Select antennas to keep using the antenna names, also select frequencies to keep.

>>> import os
>>> import numpy as np
>>> from pyuvdata import UVCal
>>> from pyuvdata.data import DATA_PATH
>>> cal = UVCal()
>>> filename = os.path.join(DATA_PATH, "zen.2458098.45361.HH.omni.calfits_downselected")
>>> cal.read_calfits(filename)

>>> # print all the antenna names with data in the original file
>>> print([cal.antenna_names[np.where(cal.antenna_numbers==a)[0][0]] for a in cal.ant_array])
['ant0', 'ant1', 'ant11', 'ant12', 'ant13', 'ant23', 'ant24', 'ant25']

>>> # print the first 10 frequencies in the original file
>>> print(cal.freq_array[0, 0:10])
[1.000000e+08 1.015625e+08 1.031250e+08 1.046875e+08 1.062500e+08
 1.078125e+08 1.093750e+08 1.109375e+08 1.125000e+08 1.140625e+08]
>>> cal.select(antenna_names=['ant11', 'ant13', 'ant25'], freq_chans=np.arange(0, 4))

>>> # print all the antenna names with data after the select
>>> print([cal.antenna_names[np.where(cal.antenna_numbers==a)[0][0]] for a in cal.ant_array])
['ant11', 'ant13', 'ant25']

>>> # print all the frequencies after the select
>>> print(cal.freq_array)
[[1.000000e+08 1.015625e+08 1.031250e+08 1.046875e+08]]

d) Select times

>>> import os
>>> import numpy as np
>>> from pyuvdata import UVCal
>>> from pyuvdata.data import DATA_PATH
>>> cal = UVCal()
>>> filename = os.path.join(DATA_PATH, "zen.2458098.45361.HH.omni.calfits_downselected")
>>> cal.read_calfits(filename)

>>> # print all the times in the original file
>>> print(cal.time_array)
[2458098.45677626 2458098.45690053 2458098.45702481 2458098.45714908
 2458098.45727336 2458098.45739763 2458098.45752191 2458098.45764619
 2458098.45777046 2458098.45789474]

>>> # select the first 3 times
>>> cal.select(times=cal.time_array[0:3])

>>> print(cal.time_array)
[2458098.45677626 2458098.45690053 2458098.45702481]

d) Select Jones components

Selecting on Jones component can be done either using the component numbers or the component strings (e.g. “Jxx” or “Jyy” for linear polarizations or “Jrr” or “Jll” for circular polarizations). If x_orientation is set on the object, strings represting the physical orientation of the dipole can also be used (e.g. “Jnn” or “ee).

>>> import os
>>> import numpy as np
>>> from pyuvdata import UVCal
>>> from pyuvdata.data import DATA_PATH
>>> import pyuvdata.utils as uvutils
>>> cal = UVCal()
>>> filename = os.path.join(DATA_PATH, "zen.2458098.45361.HH.omni.calfits_downselected")
>>> cal.read_calfits(filename)

>>> # Jones component numbers can be found in the jones_array
>>> print(cal.jones_array)
[-5 -6]

>>> # Jones component numbers can be converted to strings using a utility function
>>> print(uvutils.jnum2str(cal.jones_array))
['Jxx', 'Jyy']

>>> # make a copy of the object and select Jones components using the component numbers
>>> cal2 = cal.copy()
>>> cal2.select(jones=[-5])

>>> # print Jones component numbers and strings after select
>>> print(cal2.jones_array)
[-5]
>>> print(uvutils.jnum2str(cal2.jones_array))
['Jxx']

>>> # make a copy of the object and select Jones components using the component strings
>>> cal2 = cal.copy()
>>> cal2.select(jones=["Jxx"])

>>> # print Jones component numbers and strings after select
>>> print(cal2.jones_array)
[-5]
>>> print(uvutils.jnum2str(cal2.jones_array))
['Jxx']

>>> # print x_orientation
>>> print(cal.x_orientation)
east

>>> # make a copy of the object and select Jones components using the physical orientation strings
>>> cal2 = cal.copy()
>>> cal2.select(jones=["Jee"])

>>> # print Jones component numbers and strings after select
>>> print(cal2.jones_array)
[-5]
>>> print(uvutils.jnum2str(cal2.jones_array))
['Jxx']

UVCal: Adding data

The __add__() method lets you combine UVCal objects along the antenna, time, frequency, and/or polarization axis.

a) Add frequencies.

>>> import os
>>> import numpy as np
>>> from pyuvdata import UVCal
>>> from pyuvdata.data import DATA_PATH
>>> cal1 = UVCal()
>>> filename = os.path.join(DATA_PATH, 'zen.2457698.40355.xx.gain.calfits')
>>> cal1.read_calfits(filename)
>>> cal2 = cal1.copy()

>>> # Downselect frequencies to recombine
>>> cal1.select(freq_chans=np.arange(0, 5))
>>> cal2.select(freq_chans=np.arange(5, 10))
>>> cal3 = cal1 + cal2
>>> print((cal1.Nfreqs, cal2.Nfreqs, cal3.Nfreqs))
(5, 5, 10)

b) Add times.

>>> import os
>>> import numpy as np
>>> from pyuvdata import UVCal
>>> from pyuvdata.data import DATA_PATH
>>> cal1 = UVCal()
>>> filename = os.path.join(DATA_PATH, 'zen.2457698.40355.xx.gain.calfits')
>>> cal1.read_calfits(filename)
>>> cal2 = cal1.copy()

>>> # Downselect times to recombine
>>> times = np.unique(cal1.time_array)
>>> cal1.select(times=times[0:len(times) // 2])
>>> cal2.select(times=times[len(times) // 2:])
>>> cal3 = cal1 + cal2
>>> print((cal1.Ntimes, cal2.Ntimes, cal3.Ntimes))
(2, 3, 5)

c) Adding in place.

The following two commands are equivalent, and act on cal1 directly without creating a third uvcal object.

>>> import os
>>> import numpy as np
>>> from pyuvdata import UVCal
>>> from pyuvdata.data import DATA_PATH
>>> cal1 = UVCal()
>>> filename = os.path.join(DATA_PATH, 'zen.2457698.40355.xx.gain.calfits')
>>> cal1.read_calfits(filename)
>>> cal2 = cal1.copy()
>>> times = np.unique(cal1.time_array)
>>> cal1.select(times=times[0:len(times) // 2])
>>> cal2.select(times=times[len(times) // 2:])
>>> cal1.__add__(cal2, inplace=True)

>>> cal1.read_calfits(filename)
>>> cal2 = cal1.copy()
>>> cal1.select(times=times[0:len(times) // 2])
>>> cal2.select(times=times[len(times) // 2:])
>>> cal1 += cal2

d) Reading multiple files.

If any of the read methods (pyuvdata.UVCal.read_calfits(), pyuvdata.UVCal.read_fhd_cal()) are given a list of files, each file will be read in succession and added to the previous.

>>> import os
>>> import numpy as np
>>> from pyuvdata import UVCal
>>> from pyuvdata.data import DATA_PATH
>>> cal = UVCal()
>>> filename = os.path.join(DATA_PATH, 'zen.2457698.40355.xx.gain.calfits')
>>> cal.read_calfits(filename)
>>> cal1 = cal.select(freq_chans=np.arange(0, 2), inplace=False)
>>> cal2 = cal.select(freq_chans=np.arange(2, 4), inplace=False)
>>> cal3 = cal.select(freq_chans=np.arange(4, 7), inplace=False)
>>> cal1.write_calfits(os.path.join('.', 'tutorial1.fits'))
>>> cal2.write_calfits(os.path.join('.', 'tutorial2.fits'))
>>> cal3.write_calfits(os.path.join('.', 'tutorial3.fits'))
>>> filenames = [os.path.join('.', f) for f
...              in ['tutorial1.fits', 'tutorial2.fits', 'tutorial3.fits']]
>>> cal.read_calfits(filenames)

>>> # For FHD cal datasets pass lists for each file type
>>> fhd_cal = UVCal()
>>> obs_testfiles = [os.path.join(DATA_PATH, f) for f
...                  in ['fhd_cal_data/1061316296_obs.sav',
...                      'fhd_cal_data/set2/1061316296_obs.sav']]
>>> cal_testfiles = [os.path.join(DATA_PATH, f) for f
...                  in ['fhd_cal_data/1061316296_cal.sav',
...                      'fhd_cal_data/set2/1061316296_cal.sav']]
>>> settings_testfiles = [os.path.join(DATA_PATH, f) for f
...                       in ['fhd_cal_data/1061316296_settings.txt',
...                           'fhd_cal_data/set2/1061316296_settings.txt']]
>>> fhd_cal.read_fhd_cal(cal_testfiles, obs_testfiles, settings_file=settings_testfiles)
diffuse_model parameter value is a string, values are different

UVCal: Sorting data along various axes

Methods exist for sorting data along all the data axes to support comparisons between UVCal objects and software access patterns.

a) Sorting along the antenna axis The pyuvdata.UVCal.reorder_antennas() method will reorder the antenna axis by sorting by antenna names or numbers, in ascending or descending order, or in an order specified by passing an index array.

>>> import os
>>> import numpy as np
>>> from pyuvdata import UVCal
>>> from pyuvdata.data import DATA_PATH
>>> cal = UVCal()
>>> filename = os.path.join(DATA_PATH, 'zen.2457698.40355.xx.gain.calfits')
>>> cal.read_calfits(filename)
>>> # Default is to order by antenna number
>>> cal.reorder_antennas()
>>> print(np.min(np.diff(cal.ant_array)) >= 0)
True
>>> # Prepend a ``-`` to the sort string to sort in descending order.
>>> cal.reorder_antennas('-number')
>>> print(np.min(np.diff(cal.ant_array)) <= 0)
True

b) Sorting along the frequency axis

The pyuvdata.UVCal.reorder_freqs() method will reorder the frequency axis by sorting by spectral windows or channels (or even just the channels within specific spectral windows). Spectral windows or channels can be sorted by ascending or descending number or in an order specified by passing an index array for spectral window or channels.

>>> import os
>>> import numpy as np
>>> from pyuvdata import UVCal
>>> from pyuvdata.data import DATA_PATH
>>> cal = UVCal()
>>> filename = os.path.join(DATA_PATH, 'zen.2457698.40355.xx.gain.calfits')
>>> cal.read_calfits(filename)
>>> # First create a multi-spectral window UVCal object:
>>> cal._set_flex_spw()
>>> cal.channel_width = np.zeros(cal.Nfreqs, dtype=np.float64) + cal.channel_width
>>> cal.Nspws = 2
>>> cal.flex_spw_id_array = np.concatenate((np.ones(cal.Nfreqs // 2, dtype=int), np.full(cal.Nfreqs // 2, 2, dtype=int)))
>>> cal.spw_array = np.array([1, 2])
>>> spw2_inds = np.nonzero(cal.flex_spw_id_array == 2)[0]
>>> spw2_chan_width = cal.channel_width[0] * 2
>>> cal.freq_array[0, spw2_inds] = cal.freq_array[0, spw2_inds[0]] + spw2_chan_width * np.arange(spw2_inds.size)
>>> cal.channel_width[spw2_inds] = spw2_chan_width

>>> # Sort by spectral window number and by frequency within the spectral window
>>> # Now the spectral windows are in ascending order and the frequencies in each window
>>> # are in ascending order.
>>> cal.reorder_freqs(spw_order="number", channel_order="freq")
>>> print(cal.spw_array)
[1 2]

>>> print(np.min(np.diff(cal.freq_array[0, np.nonzero(cal.flex_spw_id_array == 1)])) >= 0)
True

>>> # Prepend a ``-`` to the sort string to sort in descending order.
>>> # Now the spectral windows are in descending order but the frequencies in each window
>>> # are in ascending order.
>>> cal.reorder_freqs(spw_order="-number", channel_order="freq")
>>> print(cal.spw_array)
[2 1]

>>> print(np.min(np.diff(cal.freq_array[0, np.nonzero(cal.flex_spw_id_array == 1)])) >= 0)
True

>>> # Use the ``select_spw`` keyword to sort only one spectral window.
>>> # Now the frequencies in spectral window 1 are in descending order but the frequencies
>>> # in spectral window 2 are in ascending order
>>> cal.reorder_freqs(select_spw=1, channel_order="-freq")
>>> print(np.min(np.diff(cal.freq_array[0, np.nonzero(cal.flex_spw_id_array == 1)])) <= 0)
True

>>> print(np.min(np.diff(cal.freq_array[0, np.nonzero(cal.flex_spw_id_array == 2)])) >= 0)
True

c) Sorting along the time axis

The pyuvdata.UVCal.reorder_times() method will reorder the time axis by sorting by time (ascending or descending) or in an order specified by passing an index array for the time axis.

>>> import os
>>> import numpy as np
>>> from pyuvdata import UVCal
>>> from pyuvdata.data import DATA_PATH
>>> cal = UVCal()
>>> filename = os.path.join(DATA_PATH, 'zen.2457698.40355.xx.gain.calfits')
>>> cal.read_calfits(filename)

>>> # Default is to order by ascending time
>>> cal.reorder_times()
>>> print(np.min(np.diff(cal.time_array)) >= 0)
True

>>> # Prepend a ``-`` to the sort string to sort in descending order.
>>> cal.reorder_times('-time')
>>> print(np.min(np.diff(cal.time_array)) <= 0)
True

d) Sorting along the Jones component axis

The pyuvdata.UVCal.reorder_jones() method will reorder the Jones component axis by the Jones component number or name, or by an explicit index ordering set by the user.

>>> import os
>>> import numpy as np
>>> from pyuvdata import UVCal
>>> from pyuvdata.data import DATA_PATH
>>> cal = UVCal()
>>> filename = os.path.join(DATA_PATH, "zen.2458098.45361.HH.omni.calfits_downselected")
>>> cal.read_calfits(filename)
>>> # Default is to order by Jones component name
>>> cal.reorder_jones()
>>> print(cal.jones_array)
[-5 -6]

UVCal: Changing cal_type from ‘delay’ to ‘gain’

UVCal includes the method pyuvdata.UVCal.convert_to_gain(), which changes a UVCal object’s cal_type parameter from “delay” to “gain”, and accordingly sets the object’s gain_array to an array consistent with its pre-existing delay_array.

>>> import os
>>> from pyuvdata import UVCal
>>> from pyuvdata.data import DATA_PATH
>>> cal = UVCal()

>>> # This file has a cal_type of 'delay'.
>>> filename = os.path.join(DATA_PATH, 'zen.2457698.40355.xx.delay.calfits')
>>> cal.read_calfits(filename)
>>> print(cal.cal_type)
delay

>>> # But we can convert it to a 'gain' type calibration.
>>> cal.convert_to_gain()
>>> print(cal.cal_type)
gain

>>> # If we want the calibration to use a positive value in its exponent, rather
>>> # than the default negative value:
>>> cal = UVCal()
>>> cal.read_calfits(filename)
>>> cal = cal.convert_to_gain(delay_convention='plus')

>>> # Convert to gain *without* running the default check that internal arrays are
>>> # of compatible shapes:
>>> cal = UVCal()
>>> cal.read_calfits(filename)
>>> cal.convert_to_gain(run_check=False)

>>> # Convert to gain *without* running the default check that optional parameters
>>> # are properly shaped and typed:
>>> cal = UVCal()
>>> cal.read_calfits(filename)
>>> cal.convert_to_gain(check_extra=False)

>>> # Convert to gain *without* running the default checks on the reasonableness
>>> # of the resulting calibration's parameters.
>>> cal = UVCal()
>>> cal.read_calfits(filename)
>>> cal.convert_to_gain(run_check_acceptability=False)