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Add caveat on 3D X-ray projector #554

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Sep 25, 2024
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Add caveat on 3D X-ray projector #554

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48dcba0
Add caveat
Michael-T-McCann Sep 19, 2024
10128bf
Try #2
Michael-T-McCann Sep 23, 2024
cbf1b90
Rephrase
Michael-T-McCann Sep 23, 2024
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8 changes: 8 additions & 0 deletions scico/linop/xray/_xray.py
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Expand Up @@ -235,6 +235,14 @@ def _calc_weights(
class XRayTransform3D(LinearOperator):
r"""General-purpose, 3D, parallel ray X-ray projector.

This projector approximates cubic voxels projecting onto
rectangular pixels and provides a back projector that is the exact
adjoint of the forward projector. It is written purely in JAX,
allowing it to run on either CPU or GPU and minimizing host copies.

Warning: This class is experimental and may be up to ten times slower
than :class:`scico.linop.xray.astra.XRayTransform3D`.
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Perhaps add some positive aspects, e.g. "It is expected to be useful for small problems as, unlike :class:scico.linop.xray.astra.XRayTransform3D, it can be run on both CPU and GPU, and the forward and adjoint transforms are differentiable." [The differentiable claim should be confirmed before inclusion!]

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Differentiable wrt to x, definitely, but so is scico.linop.xray.astra.XRayTransform3D in the way we've wrapped it. I'm not sure about differentiable wrt to the angles. I'd like to call that out of scope for this PR.

How about

This projector approximates cubical voxels projecting onto rectangular pixels and provides a back projector that is the true adjoint of the forward projector. It is written purely in JAX, allowing it to run on either CPU or GPU and minimizing host copies.

Warning: This class is experimental and may be up to ten times slower than scico.linop.xray.astra.XRayTransform3D.


For each view, the projection geometry is specified by an array
with shape (2, 4) that specifies a :math:`2 \times 3` projection
matrix and a :math:`2 \times 1` offset vector. Denoting the matrix
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