From 3a7b1505532ac64596872c54439732035955225e Mon Sep 17 00:00:00 2001
From: Michael B Kuhn <31661049+mbkuhn@users.noreply.github.com>
Date: Tue, 17 Sep 2024 08:51:12 -0600
Subject: [PATCH] Docs: add note about derived quantities (io) (#1245)

---
 docs/sphinx/user/features.rst  |  2 +-
 docs/sphinx/user/inputs_io.rst | 21 +++++++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/docs/sphinx/user/features.rst b/docs/sphinx/user/features.rst
index ef4a092e81..408b74d433 100644
--- a/docs/sphinx/user/features.rst
+++ b/docs/sphinx/user/features.rst
@@ -138,7 +138,7 @@ Flow physics
 
    * Field plane averaging and second and third order moments
 
-   * Derived fields and field operators such as vorticity, q-criterion, strain-rates, gradients, divergence, laplacian
+   * Derived fields and field operators such as vorticity, q-criterion, strain-rates, gradients, divergence, laplacian [:ref:`inp <inputs_io_derived>`]
 
    * in-situ post-processing with Ascent
 
diff --git a/docs/sphinx/user/inputs_io.rst b/docs/sphinx/user/inputs_io.rst
index 06ee37e9de..4c513ef40c 100644
--- a/docs/sphinx/user/inputs_io.rst
+++ b/docs/sphinx/user/inputs_io.rst
@@ -60,6 +60,27 @@ controls when these files are output.
 
    Add variable names to this input argument to add them to the plotfile output. These must be variables that exist in the simulation and consist of integers (not real numbers).
 
+.. _inputs_io_derived:
+
+.. input_param:: io.derived_outputs
+
+   **type:** List of strings, optional, default = ""
+
+   Add derived variable names to this input argument
+   to add them to the plotfile output. These are derived
+   quantities that are functions of real variables that exist
+   in the simulation. Currently, the available derived quantity definitions
+   that operate on the velocity field are vorticity magnitude 
+   (``mag_vorticity``), q-criterion (``q_criterion``),
+   nondimensional q-criterion (``q_criterion_nondim``),
+   and strain rate magnitude (``mag_strainrate``). Generic
+   derived quantity definitions, which operate on fields specified as an argument,
+   include the gradient operator (``grad``), the divergence
+   operator (``div``), the laplacian operator (``laplacian``),
+   and components (``components``), which isolates the specified
+   component of a field.
+
+
 .. input_param:: io.skip_outputs
 
    **type:** List of strings, optional, default = ""