Simulink interface overview in MATLAB - Mini Project: Build & Apply

Simulink Interface Overview

📖 Scenario: You are working on a simple control system project. You want to understand how to interact with Simulink models using MATLAB code. This will help you automate tasks like opening models, running simulations, and extracting results.

🎯 Goal: Build a small MATLAB script that opens a Simulink model, sets a simulation stop time, runs the simulation, and retrieves the simulation output.

📋 What You'll Learn

Create a variable with the Simulink model name

Set the simulation stop time using a variable

Use the sim function to run the model simulation

Extract the simulation output from the simulation result

Display the simulation output

💡 Why This Matters

🌍 Real World

Automating Simulink simulations saves time and reduces manual errors when testing control systems or signal processing models.

💼 Career

Many engineering and data science jobs require running and analyzing simulations efficiently using MATLAB and Simulink interfaces.

1

Create a variable for the Simulink model name

Create a variable called modelName and set it to the string 'simple_model' which is the name of the Simulink model you want to work with.

MATLAB

# Your code here

Hint

Use single quotes to define the string in MATLAB.

2

Set the simulation stop time

Create a variable called stopTime and set it to the string '10' to specify the simulation stop time in seconds.

MATLAB

modelName = 'simple_model';
# Your code here

Hint

The stop time must be a string when used in Simulink simulation settings.

3

Run the simulation using the sim function

Use the sim function with the variables modelName and stopTime to run the simulation. Store the result in a variable called simOut. Use the syntax: simOut = sim(modelName, 'StopTime', stopTime);

MATLAB

modelName = 'simple_model';
stopTime = '10';
# Your code here

Hint

The sim function runs the model and returns simulation data.

4

Extract and display the simulation output

Extract the simulation output data from simOut by accessing the yout property. Store it in a variable called simData. Then, display simData using disp(simData).

MATLAB

modelName = 'simple_model';
stopTime = '10';
simOut = sim(modelName, 'StopTime', stopTime);
# Your code here

Hint

The yout property contains the simulation output signals.

Practice

1. What is the primary purpose of the Simulink interface in MATLAB?

easy

A. To write low-level assembly code

B. To build system models visually using blocks

C. To create 3D animations

D. To perform statistical data analysis

Solution

1. Step 1: Understand Simulink's role

   Simulink is designed for visual modeling of systems using blocks.

2. Step 2: Compare options

   Options B, C, and D describe unrelated tasks to Simulink's main function.

3. Final Answer:

   To build system models visually using blocks -> Option B

4. Quick Check:

   Simulink = Visual block modeling [OK]

Hint: Simulink is about visual block diagrams, not coding [OK]

Common Mistakes:

• Confusing Simulink with MATLAB scripting
• Thinking Simulink is for data analysis
• Assuming Simulink creates animations

2. Which MATLAB command is used to open a Simulink model named myModel?

easy

A. open('myModel.slx')

B. sim('myModel')

C. load('myModel')

D. run('myModel')

Solution

1. Step 1: Identify command to open model

   The open command with the model filename opens the Simulink model.

2. Step 2: Differentiate other commands

   sim runs the model, load loads variables, run executes scripts.

3. Final Answer:

   open('myModel.slx') -> Option A

4. Quick Check:

   Open model = open('filename') [OK]

Hint: Use open('model.slx') to open Simulink models [OK]

Common Mistakes:

• Using sim() to open instead of run the model
• Confusing load() with open()
• Trying run() which is for scripts

3. What will be the output of the following MATLAB commands?

open_system('vdp');
sim('vdp');
logsout.getElement(1).Values.Data(end)

Assuming vdp is a valid Simulink model and simulation runs successfully.

medium

A. The total simulation time

B. An error because open_system does not run the model

C. The last data value from the first logged signal of the simulation

D. The initial value of the simulation signal

Solution

1. Step 1: Understand commands

   open_system('vdp') opens the model, sim('vdp') runs it, and logsout.getElement(1).Values.Data(end) accesses the last data point of the first logged signal.

2. Step 2: Interpret output

   The command returns the final value of the first signal logged during simulation.

3. Final Answer:

   The last data value from the first logged signal of the simulation -> Option C

4. Quick Check:

   sim() runs model, logsout returns data [OK]

Hint: sim() runs model; logsout stores signals [OK]

Common Mistakes:

• Thinking open_system runs the model
• Confusing signal data with simulation time
• Accessing initial instead of last data point

4. You try to run sim('myModel') but get an error: Undefined function or variable 'myModel'. What is the most likely cause?

medium

A. The model file myModel.slx is not in the current folder or MATLAB path

B. You forgot to open the model first with open_system

C. The sim command only works with built-in models

D. The model name must be in uppercase letters

Solution

1. Step 1: Analyze error message

   The error indicates MATLAB cannot find the model file named 'myModel'.

2. Step 2: Identify cause

   This usually happens if the model file is not in the current folder or MATLAB path.

3. Final Answer:

   The model file myModel.slx is not in the current folder or MATLAB path -> Option A

4. Quick Check:

   File location missing causes undefined variable error [OK]

Hint: Ensure model file is in current folder or path [OK]

Common Mistakes:

• Assuming open_system must be called before sim
• Thinking sim only works on built-in models
• Believing model names must be uppercase

5. You want to programmatically change the value of a block parameter named Gain in a Simulink model controlSys before running the simulation. Which sequence of commands correctly does this?

hard

A. load_system('controlSys'); set_param('controlSys', 'Gain', '5'); sim('controlSys');

B. open_system('controlSys'); set_param('Gain', 'Gain', 5); sim('controlSys');

C. sim('controlSys', 'Gain', 5);

D. set_param('controlSys/Gain', 'Gain', '5'); sim('controlSys');

Solution

1. Step 1: Identify correct set_param usage

   The set_param function requires the full block path and parameter name as strings. 'controlSys/Gain' is the block path, 'Gain' is the parameter, and '5' is the new value as a string.

2. Step 2: Confirm simulation command

   After setting the parameter, sim('controlSys') runs the model with updated parameters.

3. Final Answer:

   set_param('controlSys/Gain', 'Gain', '5'); sim('controlSys'); -> Option D

4. Quick Check:

   set_param with full path + sim() runs updated model [OK]

Hint: Use set_param('model/block', 'param', 'value') before sim() [OK]

Common Mistakes:

• Using set_param without full block path
• Passing numeric value instead of string for parameter
• Trying to pass parameters directly in sim()