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Updating the documentation for ramp fitting wrt the likelihood algori…
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kmacdonald-stsci committed Sep 19, 2024
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17 changes: 9 additions & 8 deletions docs/stcal/ramp_fitting/description.rst
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Expand Up @@ -19,8 +19,9 @@ using the array-based functionality of numpy. The size of the block depends
on the image size and the number of groups.


There is also a likelihood algorithm implementing an algorithm based on the group
differences of a ramp. See the detailed description below.
There is also a new algorithm available for testing, the likelihood
algorithm, implementing an algorithm based on the group differences
of a ramp. See :ref:`likelihood algorithm <likelihood_algo>`.

.. _ramp_output_products:

Expand Down Expand Up @@ -320,6 +321,8 @@ that pixel will be flagged as JUMP_DET in the corresponding integration in the
"rateints" product. That pixel will also be flagged as JUMP_DET in the "rate"
product.

.. _likelihood_algo:

Likelihood Algorithm Details
----------------------------
As an alternative to the OLS algorithm, a likelihood algorithm can be selected
Expand Down Expand Up @@ -348,11 +351,9 @@ The covariance matrix :math:`C` is a tridiagonal matrix, due to the nature of th
differences. Because the covariance matrix is tridiagonal, the computational
complexity reduces from :math:`O(n^3)` to :math:`O(n)`. To see the detailed
derivation and computations implemented, refer to the links above.
The Poisson and read noise computations are based on equations (27) and (28),
in the first link below, defining :math:`\alpha_i`, the diagonal of :math:`C`,
and :math:`\beta_i`, the off diagonal.

The full details of the algorithm can be found here:
The Poisson and read noise computations are based on equations (27) and (28), in
`Brandt (2024) <https://iopscience.iop.org/article/10.1088/1538-3873/ad38d9>`__
and

For more details, especially for the jump detection portion in the liklihood
algorithm, see
`Brandt (2024) <https://iopscience.iop.org/article/10.1088/1538-3873/ad38da>`__.

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