From dc9baee79ae3cb6b081ea1ac82e772d50afc750a Mon Sep 17 00:00:00 2001
From: Mike McCann <57153404+Michael-T-McCann@users.noreply.github.com>
Date: Wed, 25 Sep 2024 10:11:12 -0600
Subject: [PATCH] Add caveat on 3D X-ray projector (#554)

* Add caveat

* Try #2

* Rephrase
---
 scico/linop/xray/_xray.py | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/scico/linop/xray/_xray.py b/scico/linop/xray/_xray.py
index 04bdabe8..770bf627 100644
--- a/scico/linop/xray/_xray.py
+++ b/scico/linop/xray/_xray.py
@@ -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`.
+
     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