name: building-simulink-models description: Builds and edits Simulink, System Composer, Stateflow, and Simscape models. Use when modifying model structure, parameters, ports, connections, or Stateflow chart internals. license: MathWorks BSD-3-Clause metadata: version: "1.1"

Building Models

Use model_edit for Simulink, System Composer, and Simscape models (structural changes and parameter configuration). For Stateflow chart internals, use evaluate_matlab_code with the Stateflow API (see below).

When to Use

• Adding, connecting, deleting, or replacing blocks in a model
• Configuring block parameters, signal properties, or model settings
• Creating or editing Stateflow chart internals (states, transitions, junctions)
• Building System Composer architecture models
• Wiring Simscape physical connections

When NOT to Use

• Querying parameter values → use model_query_params
• Resolving variable references to numeric values → use model_resolve_params

Workflow

1. Read first: Use model_read on the target scope to get block IDs and understand existing topology.
2. Plan the data flow: For complex edits, sketch inputs → operations → outputs, then map to blocks.
3. Edit: Use model_edit with operations scoped to one subsystem level at a time.
4. Verify: Use model_read on the scope to confirm the structure matches your intent.

CRITICAL: If model_edit returns status: partial, run model_read immediately to determine if corrective action is needed.

Operation Chaining with ref

Use ref to name a block and #ref to reference it in later operations within the same call:

[{"op": "add_block", "type": "Gain", "name": "MyGain", "ref": "g1"},
 {"op": "connect", "target": "blk_5.y1 -> #g1.u1"}]

The response created map shows ref → blk_id. In subsequent calls, use the blk_id (e.g., blk_42) — #ref only works within a single call.

Guardrails

• Never manually construct block path strings from names shown in model_overview or model_read. Block names can contain invisible newlines and trailing whitespace that cause hilite_system, open_system, and get_param to fail. Instead, resolve paths from blk_X IDs:

  % blk_42 → use the number after "blk_" as the SID
  blockPath = Simulink.ID.getFullName('<ModelName>:42');
  hilite_system(blockPath)
  open_system(blockPath)
  get_param(blockPath, 'BlockType')
  

• Do not call Simulink.BlockDiagram.arrangeSystem or use set_param for block positioning unless the user explicitly requests it. model_edit has a built-in autolayout engine that runs automatically after each call.
• Always pass layout_mode to model_edit. Use "full" when populating an empty scope (new model root, or a newly-created subsystem) for optimal block arrangement. Use "incremental" when adding blocks to a scope that already has existing blocks (preserves existing positions).
• Use meaningfully named variables (e.g., Kp_SpeedController) instead of hardcoded numeric values. Define variables in model workspace or a .m init script.
• Don't use evaluate_matlab_code with set_param/add_block to bypass model_edit — it skips autolayout, undo tracking, and error recovery
• Use open_system rather than load_system to open models that are not already open, or when creating new models, unless the user explicitly asks otherwise or the model is a library. This ensures the user can see live edits as they happen.

Naming Conventions

Prefer code-generation-safe names for blocks, signals, and variables:

• Use only: a-z, A-Z, 0-9, underscore (_)
• Don't start with a number
• Don't use leading/trailing or consecutive underscores
• Prefer names under 32 characters (required for some code generation targets)

Block Types

Use the block's display name in the type field. Do not construct or guess library paths.

• Built-in Simulink blocks: Use the BlockType directly: Gain, Sum, Constant, Integrator, SubSystem, Scope
• Library blocks (Simscape, Aerospace, DSP, Communications, etc.): Use the display name as it appears in the Simulink Library Browser: Voltage Source, Resistor, DC Motor, Solver Configuration, 6DOF (Euler Angles)
• If model_edit returns INVALID_TYPE: Fall back to the full library path from MATLAB documentation (e.g., ee_lib/Sources/Voltage Source)

[{"op": "add_block", "type": "Voltage Source", "name": "V1", "ref": "v1"},
 {"op": "add_block", "type": "Resistor", "name": "R1", "ref": "r1"},
 {"op": "add_block", "type": "Electrical Reference", "name": "Gnd", "ref": "gnd"},
 {"op": "add_block", "type": "Solver Configuration", "name": "Solver", "ref": "sc"}]

Domain-Specific Rules

When working with these domains, read the corresponding reference file before editing:

• Stateflow charts -> reference/stateflow.md — model_edit can add Chart blocks but cannot edit chart internals. Use evaluate_matlab_code with the Stateflow API for states, transitions, junctions, and data. The reference covers API gotchas, subcharts, lint checks, and layout.
• System Composer architecture models -> reference/system-composer.md — Create models with systemcomposer.createModel, then use model_edit. Components use type: "SubSystem", ports use Bus Element blocks. The reference covers component creation, port wiring, and behavior model generation.
• Simscape physical models -> reference/simscape.md — Physical connections use bidirectional <-> syntax. The reference covers connection semantics, port patterns, and initial target variables.