Add missing API documentation for all exported symbols

docs/pages.jl

@@ -47,5 +47,8 @@ pages = [
         "basics/Precompilation.md",
         "basics/FAQ.md"],
     "comparison.md",
-    "internals.md"
+    "Internal Details" => Any[
+        "internals.md",
+        "internals/structural_transformation.md",
+        "internals/bipartite_graph.md"]
 ]

docs/src/API/System.md

@@ -224,3 +224,27 @@ following functions are useful for manipulating namespacing functionality.
 ModelingToolkit.renamespace
 ModelingToolkit.namespace_equations
 ```
+
+## Linearization and Analysis
+
+Functions for linearization and analysis of systems.
+
+```@docs
+linearization_ap_transform
+get_sensitivity_function
+get_comp_sensitivity_function
+get_looptransfer_function
+get_sensitivity
+get_comp_sensitivity
+get_looptransfer
+open_loop
+```
+
+## Additional Equation Classification
+
+```@docs
+alg_equations
+diff_equations
+has_alg_equations
+has_diff_equations
+```

docs/src/internals.md

@@ -1,4 +1,16 @@
 # Internal Details
 
-This is a page for detailing some of the inner workings to help future
-contributors to the library.
+This section documents the internal implementation details of ModelingToolkit. These APIs are not considered stable and may change without notice in non-breaking releases. They are documented here to help future contributors understand the library's inner workings.
+
+## Overview
+
+ModelingToolkit's internal architecture consists of several key components:
+
+- **Structural Transformation**: Algorithms for transforming equation systems, including index reduction, tearing, and algebraic simplification
+- **Bipartite Graphs**: Graph representations used to analyze relationships between equations and variables
+- **System Structure**: Internal representations of system state and transformations
+
+These components work together to enable ModelingToolkit's symbolic manipulation and code generation capabilities.
+
+!!! warning
+    The functions and types documented in this section are internal implementation details. Users should not rely on these APIs as they may change or be removed without deprecation warnings.

docs/src/internals/bipartite_graph.md

@@ -0,0 +1,80 @@
+# Bipartite Graphs
+
+!!! warning "Internal API"
+    The functions documented on this page are internal implementation details of ModelingToolkit. They are not part of the public API and may change or be removed without notice in non-breaking releases. This documentation is provided to help contributors understand the codebase.
+
+ModelingToolkit uses bipartite graphs to represent relationships between equations and variables in systems. These functions provide tools for working with and analyzing these graphs.
+
+## Graph Types
+
+```@docs
+BipartiteGraph
+BipartiteEdge
+DiCMOBiGraph
+DiffGraph
+```
+
+## Vertex Operations
+
+```@docs
+𝑠vertices
+𝑑vertices
+has_𝑠vertex
+has_𝑑vertex
+nsrcs
+ndsts
+```
+
+## Neighbor Operations
+
+```@docs
+𝑠neighbors
+𝑑neighbors
+set_neighbors!
+```
+
+## Edge Operations
+
+```@docs
+𝑠edges
+𝑑edges
+```
+
+## Graph Views and Modifications
+
+```@docs
+invview
+delete_srcs!
+delete_dsts!
+```
+
+## Matching Algorithms
+
+```@docs
+maximal_matching
+construct_augmenting_path!
+```
+
+## Dependency Analysis
+
+```@docs
+equation_dependencies
+variable_dependencies
+eqeq_dependencies
+varvar_dependencies
+map_variables_to_equations
+```
+
+## Graph Conversion
+
+```@docs
+asgraph
+asdigraph
+```
+
+## Constants
+
+```@docs
+SRC
+DST
+```

docs/src/internals/structural_transformation.md

@@ -0,0 +1,87 @@
+# Structural Transformation
+
+!!! warning "Internal API"
+    The functions documented on this page are internal implementation details of ModelingToolkit. They are not part of the public API and may change or be removed without notice in non-breaking releases. This documentation is provided to help contributors understand the codebase.
+
+These functions are used for structural analysis and transformation of equation systems, including index reduction, tearing, and other algebraic manipulations used in the simplification process.
+
+## Tearing and Algebraic Simplification
+
+```@docs
+tearing
+tearing_reassemble
+tearing_substitution
+torn_system_jacobian_sparsity
+find_solvables!
+linear_subsys_adjmat!
+```
+
+## Index Reduction
+
+```@docs
+dae_index_lowering
+pantelides!
+pantelides_reassemble
+dummy_derivative
+```
+
+## Consistency Checking
+
+```@docs
+check_consistency
+```
+
+## Incidence Matrix Operations
+
+```@docs
+sorted_incidence_matrix
+but_ordered_incidence
+```
+
+## Variable Ordering and Masks
+
+```@docs
+lowest_order_variable_mask
+highest_order_variable_mask
+computed_highest_diff_variables
+```
+
+## Shift Operations
+
+These functions handle shift operations in discrete-time systems.
+
+```@docs
+shift2term
+lower_shift_varname
+simplify_shifts
+distribute_shift
+```
+
+## System Structure Types and Functions
+
+```@docs
+SystemStructure
+TearingState
+TransformationState
+isdiffvar
+isdervar
+isalgvar
+isdiffeq
+algeqs
+is_only_discrete
+dervars_range
+diffvars_range
+algvars_range
+get_fullvars
+system_subset
+```
+
+## Graph Types
+
+```@docs
+Matching
+InducedCondensationGraph
+MatchedCondensationGraph
+Unassigned
+unassigned
+```