Running a simulation in Simulink - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding simulation stop time in Simulink

In Simulink, what does setting the Stop time parameter control during a simulation?

A The total duration for which the simulation runs before stopping automatically.

B The time interval between each simulation step.

C The initial time from which the simulation starts.

D The maximum number of iterations the solver performs.

💡 Hint

Think about how long you want your simulation to run in real time.

The Stop time sets the total simulation duration. The simulation runs from the start time (usually 0) up to this stop time.

❓ Predict Output

intermediate

Output of a simple Simulink simulation run command

What is the output of the following MATLAB command after running a Simulink model named 'simple_model'?

simOut = sim('simple_model');
disp(simOut.tout(end));

A The total number of simulation steps performed.

B The initial simulation time, usually 0.

C An error because 'simOut' does not contain 'tout'.

D The final simulation time value, equal to the model's Stop time.

💡 Hint

Check what simOut.tout stores in Simulink simulation output.

simOut.tout is a vector of time points during simulation. The last element tout(end) is the final simulation time, which matches the Stop time.

❓ data_output

advanced

Analyzing simulation output data structure

After running a Simulink simulation with output logged to workspace, what is the structure of the variable simOut.logsout?

A A table with time stamps as rows and signals as columns.

B A cell array of strings naming each logged signal.

C A Simulink.SimulationData.Dataset object containing logged signals as elements.

D A numeric array with all logged signal values concatenated.

💡 Hint

Consider how Simulink organizes multiple logged signals in the workspace.

logsout is a Dataset object that holds each logged signal as an element with its own time and data.

🔧 Debug

advanced

Identifying cause of simulation stop error

During a Simulink simulation, the error "Simulation stopped unexpectedly at time 5.0" appears. Which of the following is the most likely cause?

A The model contains algebraic loops that the solver cannot resolve.

B The Stop time parameter is set to 0.

C The simulation ran successfully without errors.

D The solver step size is larger than the Stop time.

💡 Hint

Think about what can cause a simulation to stop before reaching the Stop time.

Algebraic loops without proper solver settings can cause the simulation to halt unexpectedly at a certain time.

🚀 Application

expert

Optimizing simulation speed with solver settings

You want to speed up a Simulink simulation of a complex model without losing significant accuracy. Which solver setting change is most appropriate?

A Decrease the maximum step size in a variable-step solver.

B Switch from a variable-step solver to a fixed-step solver with a larger step size.

C Use a variable-step solver with a very small minimum step size.

D Disable all solver diagnostics to reduce overhead.

💡 Hint

Consider how step size affects simulation speed and accuracy.

Using a fixed-step solver with a larger step size reduces the number of calculations, speeding up simulation while maintaining acceptable accuracy for many models.

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