Simulink Frequency Response Estimation

Obtain frequency response data from Simulink models using simulation-based estimation (frestimate) when analytical linearization is not viable or as a validation tool.

When to Use

• Model contains hard discontinuities (PWM, switching, relay, quantizer) that linearize to zero or NaN
• Validating a linear model against a simulation based linearization of a Simulink model
• Estimating frequency response directly from simulation data

When NOT to Use

• Model linearizes cleanly with linearize, use simulink-linearize instead
• Working with measured data only (no Simulink model), use System Identification Toolbox

Workflow

1. Define I/O  →  2. Choose Signal  →  3. Configure  →  4. Estimate  →  5. Fit (optional)
   (linio)          (PRBS/Sinestream)    (constraints)    (frestimate)     (tfest)

Stage 1: Define I/O Points

Determine I/O points for the estimation using this decision sequence. Use the first case that applies:

Case A, IO points can be inferred from prompt or model context:

Use the first sub-case that matches:

1. User specifies explicit I/O signals or blocks (e.g., "from r to y") → define linio points. All linio points must reference a block's output port. If a candidate block has no output ports (Outport, Terminator, Scope) → trace upstream to find the source block and port with model_read.

   io = [linio(sprintf("%s/InputBlock", mdl), 1, "input"); ...
         linio(sprintf("%s/OutputBlock", mdl), 1, "output")];
   

2. Root-level Inport/Outport blocks exist → use model_read at root scope (depth "0") to identify root-level Inport/Outport blocks, then define linio at those blocks (trace Outport blocks upstream to their source for the output linio point).

Case B, Cannot determine IO points: