diff --git a/docs/sphinx/devel/about_doc.rst b/docs/sphinx/devel/about_doc.rst
index 22c4cf828704bc1101b9bbf37224bb7c8b304003..e846e8355e2c518728b43844b8382ca368e401d4 100644
--- a/docs/sphinx/devel/about_doc.rst
+++ b/docs/sphinx/devel/about_doc.rst
@@ -3,9 +3,8 @@
 How to document classes in HySoP
 =================================
 
-We try to fit as much as possible with `numpydoc guide <https://github.com/numpy/numpy/blob/master/doc/HOWTO_DOCUMENT.rst.txt>`
+We try to fit as much as possible with `numpydoc guide <https://numpydoc.readthedocs.io/en/latest/>`
 guide standards.
 
 See the files fields/continuous.py and operator/drag_and_lift.py which are used as reference files for documentation
-and 
-
+and
diff --git a/docs/sphinx/devel/about_operators_graph.rst b/docs/sphinx/devel/about_operators_graph.rst
new file mode 100644
index 0000000000000000000000000000000000000000..2ba3dfd61b7a4f6f31c06ef99f8f2ac5c2bb0600
--- /dev/null
+++ b/docs/sphinx/devel/about_operators_graph.rst
@@ -0,0 +1,45 @@
+.. _about_operators_graph:
+
+How HySoP deals with computational graphs of operators
+======================================================
+
+.. inheritance-diagram::
+   hysop.core.graph.computational_node.ComputationalGraphNode
+   hysop.core.graph.computational_graph.ComputationalGraph
+   hysop.core.graph.node_generator.ComputationalGraphNodeGenerator
+   hysop.core.graph.computational_operator.ComputationalGraphOperator
+   hysop.core.graph.computational_node_frontend.ComputationalGraphNodeFrontend
+   hysop.operator.directional.directional.DirectionalOperatorBase
+   hysop.operator.directional.directional.DirectionalOperatorGenerator
+   hysop.operator.directional.directional.DirectionalOperatorFrontend
+   hysop.numerics.splitting.directional_splitting.DirectionalSplitting
+   hysop.problem.Problem
+   :parts: 1
+   :caption: Inheritance diagram for HySoP computational graphs.
+
+
+HySoP library is designed for the user to manipulate only operators
+and problems. It internally build a directed graph of operators (low level
+computations or data operations) for running a single a solver
+iteration. Therefore, solving a Problem means running iteratively the
+graph traversal. Order of inserting elements in the Problem using
+:meth:`~hysop.problem.Problem.insert` (or graph  using :meth:`~hysop.core.graph.computational_graph.ComputationalGraph.push_nodes`)
+is important.
+
+Two kind of object can be inserted into a graph:
+
+- a :class:`~hysop.core.graph.computational_node.ComputationalGraphNode` by means of:
+
+  * an operator (:class:`~hysop.core.graph.computational_operator.ComputationalGraphOperator`)
+  * a sub-graph (:class:`~hysop.core.graph.computational_graph.ComputationalGraph`) when using a operator of operators
+
+- an operator generator (:class:`~hysop.core.graph.node_generator.ComputationalGraphNodeGenerator` or
+  :class:`~hysop.core.graph.computational_node_frontend.ComputationalGraphNodeFrontend`). In that case, only generated
+  operators are inserted into graph, the generator itself is not inserted.
+
+We distinguish directional operators from operators. Directional
+operators must split into several operators (at least one per spatial
+directions) using a :class:`~hysop.numerics.splitting.directional_splitting.DirectionalSplitting`. The nested
+operators are sharing a common basis:
+:class:`~hysop.operator.directional.directional.DirectionalOperatorBase` that are generated by :class:`~hysop.operator.directional.directional.DirectionalOperatorGenerator`. Directional operators generators will automatically insert also
+transposition operators (see :ref:`about_work_arrays`).
diff --git a/docs/sphinx/devel/index.rst b/docs/sphinx/devel/index.rst
index 660c466335a11edf864680c296aed9dc49aa7d83..2eef3e21d7b6b4314f300b3c6022680ef804985c 100644
--- a/docs/sphinx/devel/index.rst
+++ b/docs/sphinx/devel/index.rst
@@ -2,7 +2,7 @@
 
 
 ############################
-HySoP Developers Guide 
+HySoP Developers Guide
 ############################
 
 This part is for developers of Hysop and provides guidelines on the "proper" ways to write python code, documentation, examples, tests ... in HySoP.
@@ -12,6 +12,11 @@ This part is for developers of Hysop and provides guidelines on the "proper" way
 
    about_doc
    coding_guidelines
+   fortran2python
+   about_operators_graph
    about_work_arrays
+   about_codegen
+   about_autotuning
+   about_symbolic
    memo_sphinx
    hysop_validation
diff --git a/docs/sphinx/index.rst.in b/docs/sphinx/index.rst.in
index a70e47b6ef165447fb4be63b39982cb68c75616d..89158201271167117b27f74454ced348e71c36f1 100644
--- a/docs/sphinx/index.rst.in
+++ b/docs/sphinx/index.rst.in
@@ -13,6 +13,7 @@ HySoP software: hybrid simulation with particles
    getting_started/index
    users_guide/index
    examples/index
+   devel/index
    reference/index
    license
    contacts
@@ -32,6 +33,3 @@ The library is mainly written in Python (high level functionnalities) and Fortra
 
    .. image:: /figures/vorticity_field.*
       :height: 200px
-
-
-