updated toc

_toc.yml

@@ -1,7 +1,10 @@
 # PBDL Table of content (cf https://jupyterbook.org/customize/toc.html)
 #
+
 - file: intro.md
-  sections:
+
+- part: Introduction
+  chapters:
   - file: intro-teaser.ipynb
   - file: overview.md
     sections:
@@ -12,10 +15,15 @@
     sections:
       - file: supervised-airfoils.ipynb
       - file: supervised-discuss.md
+
+- part: Physical Losses
+  chapters:
   - file: physicalloss.md
-  sections:
   - file: physicalloss-code.ipynb
   - file: physicalloss-discuss.md
+
+- part: Differentiable Physics
+  chapters:
   - file: diffphys.md
     sections:
       - file: diffphys-code-burgers.ipynb
@@ -27,11 +35,17 @@
       - file: diffphys-code-sol.ipynb
       - file: diffphys-control.ipynb
       - file: diffphys-outlook.md
+
+- part: Physical Gradients
+  chapters:
   - file: physgrad.md
     sections:
       - file: physgrad-comparison.ipynb
       - file: physgrad-nn.md
       - file: physgrad-discuss.md
+  
+- part: End Matter
+  chapters:
   - file: outlook.md
   - file: old-phiflow1.md
     sections:
@@ -44,3 +58,6 @@
       - file: diffphys-code-ns-v2a.ipynb
   - file: references.md
   - file: notation.md
+  
+  
+