Jacobian computation

The original cgi-howfsc loop code comes with several options on when and how to compute the Jacobian matrix and related data. These can be called in the same way on the corgihowfsc repo, where the relevant loop code is encapsulated in the function nulling_gitl(), located in corgihowfsc/gitl/nulling_gitl.py. The original function on cgi-howfsc that does this can be found here.

The files relating to a Jacobian input are:

• The Jacobian matrix

• The JTWJ map, which is the weighting map W (J^T * W * J) as it is used in the EFC algorithm; more info here.

• The n2clist, which is a list of conversion factors from normalized intensity to contrast. For more info see here.

Jacobian strategies

The different Jacobian strategies represent different choice for when which of the above files are precomputed for the loop and loaded from disk, or computed at runtime.

Note

There are four Jacobian strategies for the HOWFSC loop:

Jacobian and JTWJ	n2clist	keyword
Load from disk, keep fixed throughout loop	Load from disk, keep fixed throughout loop	load_all
Compute before loop, keep fixed throughout loop	Load from disk, keep fixed throughout loop	precomp_jacs_once
Compute before each iteration	Load from disk, keep fixed throughout loop	precomp_jacs_always
Compute before loop, keep fixed throughout loop	Compute before loop, keep fixed throughout loop	precomp_all_once

The above are the three options fed into the precomp variable of the top-level HOWFSC function called nulling_gitl() called in the launcher script.

Important

CGI is anticipated to calculate Jacobians at each iteration, which is why this is the default option in corgihowfsc.

Original docstring from git_howfsc repo:
See original docstrings in the roman-corgi/cgi-howfsc repo here.

precomp : str, optional
    One of 'load_all', 'precomp_jacs_once', 'precomp_jacs_always',
    or 'precomp_all_once'.  This determines how the Jacobians and related
    data are handled.  Defaults to 'load_all'.
    'load_all' means that the Jacobians, JTWJ map, and n2clist are all
    loaded from files in jacpath and leaves them fixed throughout a loop.
    'precomp_jacs_once' means that the Jacobians and JTWJ map are computed
    once at the start of the sequence, and the n2clist is loaded from files
    in jacpath.
    'precomp_jacs_always' means that the Jacobians and JTWJ map are computed
    at the start of the sequence and then recomputed at the start of every
    iteration except the last one; the n2clist is loaded from files in jacpath.
    'precomp_all_once' means that the Jacobians, JTWJ map, and n2clist are
    all computed once at the start of the sequence.

Precomputing a Jacobian

To calculate a Jacobian outside of the loop, you can use the script/make_jacobian.py script.

Note

The Jacobian is always computed using the compact model.

The resulting file has a size of 2.2 GB inside the jacobians folder under the corgi_loop base folder, located in your home directory.

You will need to rename your Jacobian for the respective coronagraph mode you want to run a loop on. For the narrow FOV mode with the HLC, rename the Jacobian to narrowfov_jac_full.fits.

The calculate_jacobian_multiprocessed() function docstring contains more information about the input parameters.

Implementation details

A bunch of implementation caveats for the corgihowfsc repo (TBD).