Running a simulation in Simulink - Step-by-Step Execution

Concept Flow - Running a simulation

Open Simulink Model

↓

Set Simulation Parameters

↓

Start Simulation

↓

Simulink Runs Model

↓

Collect Output Data

↓

Analyze or Visualize Results

↓

Stop Simulation

The flow shows opening a model, setting parameters, running the simulation, collecting data, and analyzing results.

Execution Sample

Simulink

sim('model_name')
% Runs the Simulink model named 'model_name'
% Collects output logged in workspace
plot(simout.time, simout.signals.values)
% Plots simulation output over time

This code runs a Simulink model and plots the output signal over time.

Execution Table

Step	Action	Evaluation	Result
1	Open model 'model_name'	Model loaded	Model ready for simulation
2	Set simulation stop time to 10 seconds	Stop time set	Simulation will run for 10 seconds
3	Start simulation with sim('model_name')	Simulation running	Model executes equations over time
4	Simulink computes outputs at each time step	Outputs generated	Output data stored in simout
5	Simulation reaches stop time	Simulation stops	Final output data available
6	Plot output data	Data plotted	Graph shows signal vs time

💡 Simulation stops when time reaches the set stop time (10 seconds)

Variable Tracker

Variable	Start	After Step 3	After Step 5	Final
simout	undefined	partial data during simulation	complete data after simulation	complete data after simulation
time	undefined	time vector growing	time vector complete	time vector complete
signal values	undefined	values computed stepwise	values complete	values complete

Key Moments - 3 Insights

Why does the simulation stop automatically after some time?

The simulation stops because the stop time parameter is set before running. See execution_table row 5 where simulation stops at 10 seconds.

What is stored in the variable 'simout'?

'simout' stores the output signals generated during simulation. It starts undefined and fills as simulation runs (see variable_tracker).

Why do we plot after simulation stops?

Plotting requires complete data. The simulation must finish to have full output data to visualize (see execution_table row 6).

Visual Quiz - 3 Questions

Look at the execution_table, at which step does the simulation actually start running?

A Step 3

B Step 1

C Step 5

D Step 6

💡 Hint

Check the 'Action' column for when sim('model_name') is called.

According to variable_tracker, what is the state of 'simout' after step 3?

A Complete data available

B Partial data during simulation

C Undefined

D Data deleted

💡 Hint

Look at the 'After Step 3' column for 'simout' in variable_tracker.

If the stop time was set to 20 seconds instead of 10, what would change in the execution_table?

A Step 6 would be skipped

B Step 3 would not run

C Step 5 would say simulation stops at 20 seconds

D Simulation would stop immediately

💡 Hint

Refer to the exit_note and step 5 about simulation stop time.

Concept Snapshot

Running a simulation in Simulink:
1. Open your model.
2. Set simulation parameters (like stop time).
3. Run simulation with sim('model_name').
4. Simulink computes outputs over time.
5. Collect output data (e.g., simout).
6. Analyze or plot results after simulation ends.

Full Transcript

Running a simulation in Simulink involves opening a model, setting parameters such as stop time, and starting the simulation using the sim function. During simulation, Simulink computes outputs step-by-step and stores them in variables like simout. The simulation stops automatically when the stop time is reached. After simulation finishes, you can analyze or plot the output data to understand the system behavior.

Practice

1. What is the main purpose of running a simulation in Simulink?

easy

A. To test and analyze a model's behavior without building physical hardware

B. To write code faster

C. To create graphical user interfaces

D. To compile the model into an executable file

Solution

1. Step 1: Understand simulation purpose

   Simulation allows testing how a model behaves in a virtual environment.

2. Step 2: Compare options

   Only To test and analyze a model's behavior without building physical hardware describes testing and analyzing without physical hardware.

3. Final Answer:

   To test and analyze a model's behavior without building physical hardware -> Option A

4. Quick Check:

   Simulation = safe model testing [OK]

Hint: Simulation means testing model behavior virtually [OK]

Common Mistakes:

• Confusing simulation with code writing
• Thinking simulation creates GUIs
• Assuming simulation compiles code

2. Which command correctly starts a simulation of a Simulink model named myModel?

easy

A. sim('myModel')

B. execute('myModel')

C. start_sim('myModel')

D. run('myModel')

Solution

1. Step 1: Recall Simulink simulation command

   The correct command to run a simulation is sim('modelName').

2. Step 2: Match command to options

   Only sim('myModel') uses sim('myModel') correctly.

3. Final Answer:

   sim('myModel') -> Option A

4. Quick Check:

   sim command runs simulation [OK]

Hint: Use sim('modelName') to start simulation [OK]

Common Mistakes:

• Using run() instead of sim()
• Trying start_sim() which is invalid
• Using execute() which is not a Simulink command

3. Given the code:

out = sim('simpleModel', 'StopTime', '10');
disp(out.tout(end));

What will be displayed?

medium

A. 0

B. 10

C. Simulation error

D. Undefined variable

Solution

1. Step 1: Understand sim command with StopTime

   The simulation runs from time 0 to 10 seconds.

2. Step 2: Check output time vector

   out.tout stores simulation time points; end is last time point, which is 10.

3. Final Answer:

   10 -> Option B

4. Quick Check:

   Simulation end time = 10 [OK]

Hint: tout(end) shows simulation stop time [OK]

Common Mistakes:

• Assuming output is 0 instead of final time
• Expecting an error without cause
• Confusing variable names

4. What is wrong with this code snippet to run a simulation?

sim('modelName', StopTime=20);

medium

A. The StopTime parameter is misspelled

B. The model name must be a variable, not a string

C. StopTime should be a string, not a variable

D. sim command cannot take parameters

Solution

1. Step 1: Check parameter syntax for sim

   Parameters like StopTime must be passed as strings: 'StopTime', '20'.

2. Step 2: Identify error in code

   Code uses StopTime=20 without quotes, causing syntax error.

3. Final Answer:

   StopTime should be a string, not a variable -> Option C

4. Quick Check:

   Parameter names and values must be strings [OK]

Hint: Use quotes for parameter names and values [OK]

Common Mistakes:

• Passing parameters without quotes
• Confusing variable and string types
• Thinking sim can't take parameters

5. You want to run a simulation of controlModel from 0 to 15 seconds and save the output to variable simOut. Which code correctly does this and allows you to access the simulation output data?

hard

A. sim('controlModel', 'StopTime', 15, 'Output', simOut);

B. sim('controlModel', 'StartTime', '0', 'EndTime', '15');

C. simOut = run('controlModel', StopTime='15');

D. simOut = sim('controlModel', 'StopTime', '15');

Solution

1. Step 1: Identify correct sim syntax for stop time and output

   Use sim('modelName', 'StopTime', 'time') and assign output to a variable.

2. Step 2: Evaluate options

   simOut = sim('controlModel', 'StopTime', '15'); correctly assigns output to simOut and sets stop time as string '15'. Others have syntax errors or wrong commands.

3. Final Answer:

   simOut = sim('controlModel', 'StopTime', '15'); -> Option D

4. Quick Check:

   Assign sim output to variable with sim('model', 'StopTime', 'time') [OK]

Hint: Assign sim output to variable; use 'StopTime' as string [OK]

Common Mistakes:

• Passing StopTime as number without quotes
• Using run() instead of sim()
• Incorrect parameter names like StartTime/EndTime