Error signal computation in Simulink - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to compute the error signal as the difference between the reference and output signals.

Simulink

error = reference [1] output

Drag options to blanks, or click blank then click option'

A+

B-

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition instead of subtraction.

Multiplying or dividing signals instead of subtracting.

The error signal is calculated by subtracting the output from the reference signal.

2fill in blank

medium

Complete the code to compute the squared error signal.

Simulink

squared_error = (error [1] 2)

Drag options to blanks, or click blank then click option'

A*

B-

C**

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using multiplication operator without parentheses.

Using addition or subtraction instead of power.

Squaring the error signal is done by raising it to the power of 2 using the '**' operator.

3fill in blank

hard

Fix the error in the code to compute the absolute error signal.

Simulink

abs_error = abs([1])

Drag options to blanks, or click blank then click option'

Aerror

Boutput - reference

Creference - output

Dreference + output

Attempts:

3 left

💡 Hint

Common Mistakes

Putting the subtraction expression inside abs() instead of the error variable.

Adding signals instead of subtracting.

The absolute error is the absolute value of the error signal, so use the variable 'error' inside abs().

4fill in blank

hard

Fill both blanks to create a dictionary that maps signal names to their error computations.

Simulink

error_signals = {"[1]": reference [2] output, "squared_error": (reference - output)**2}

Drag options to blanks, or click blank then click option'

Aerror

B-

C+

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' instead of '-' for error calculation.

Using incorrect key names.

The dictionary key 'error' maps to the difference between reference and output, which is reference - output.

5fill in blank

hard

Fill both blanks to compute mean squared error from a list of errors.

Simulink

mse = sum([e[1] for e in errors]) [2] len(errors)

Drag options to blanks, or click blank then click option'

A**2

B/

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to square each error.

Using multiplication instead of division.

Adding extra operators after len(errors).

Each error is squared (e**2), summed, then divided by the number of errors to get the mean squared error. The last blank is empty because no operator is needed after len(errors).

Practice

1. What does the error signal represent in Simulink models?

easy

A. The multiplication of input and output signals

B. The sum of all output signals

C. The delay between input and output

D. The difference between the desired and actual output values

Solution

1. Step 1: Understand the definition of error signal and match to options

   The error signal is defined as the difference between what is desired (reference) and what is actually produced (output). The difference between the desired and actual output values correctly states this difference, while others describe unrelated operations.

2. Final Answer:

   The difference between the desired and actual output values -> Option D

3. Quick Check:

   Error signal = desired - actual [OK]

Hint: Error signal = desired value minus actual output [OK]

Common Mistakes:

• Confusing error with sum or product of signals
• Thinking error is a delay or time difference
• Mixing input and output signals

2. Which Simulink block is commonly used to compute the error signal?

easy

A. Gain block to multiply signals

B. Integrator block to accumulate signals

C. Sum block with configuration to subtract output from reference

D. Scope block to display signals

Solution

1. Step 1: Identify block for error calculation and eliminate others

   The Sum block can be configured to subtract one input from another, which matches error signal computation. Gain multiplies, Integrator accumulates, Scope only displays signals, so they do not compute error.

2. Final Answer:

   Sum block with configuration to subtract output from reference -> Option C

3. Quick Check:

   Sum block subtracts signals for error [OK]

Hint: Use Sum block set to subtract for error calculation [OK]

Common Mistakes:

• Choosing Gain block which multiplies instead of subtracts
• Confusing Scope as a computation block
• Using Integrator which accumulates rather than subtracts

3. Given the following Simulink signals: Reference = [5, 7, 9], Output = [3, 7, 10]. What is the error signal computed as Reference - Output?

medium

A. [2, 0, -1]

B. [8, 14, 19]

C. [-2, 0, 1]

D. [3, 7, 10]

Solution

1. Step 1: Subtract output values from reference values element-wise

   Calculate 5-3=2, 7-7=0, 9-10=-1. The resulting error signal is [2, 0, -1].

2. Final Answer:

   [2, 0, -1] -> Option A

3. Quick Check:

   Error = Reference - Output = [2, 0, -1] [OK]

Hint: Subtract output from reference element-wise for error [OK]

Common Mistakes:

• Adding instead of subtracting signals
• Mixing order: output - reference instead of reference - output
• Copying output values as error

4. A Simulink model uses a Sum block to compute error as Reference + Output. What is the issue with this setup?

medium

A. Reference and Output cannot be inputs to the same block

B. The error signal should be Reference minus Output, not their sum

C. Output should be subtracted from Reference using a Gain block

D. Sum block cannot add signals

Solution

1. Step 1: Understand correct error signal formula and identify setup issue

   Error signal is Reference minus Output, so adding them is incorrect. Sum block configured to add will produce wrong error values, leading to incorrect control or training.

2. Final Answer:

   The error signal should be Reference minus Output, not their sum -> Option B

3. Quick Check:

   Error = Reference - Output, not Reference + Output [OK]

Hint: Sum block must subtract output from reference for error [OK]

Common Mistakes:

• Configuring Sum block to add instead of subtract
• Using Gain block unnecessarily for subtraction
• Assuming inputs cannot be connected to same block

5. In a control system modeled in Simulink, the error signal is computed as Reference - Output. If the Reference signal is constant at 10 and the Output signal fluctuates as [8, 12, 9, 11], what is the correct error signal sequence, and why is this important for system performance?

hard

A. [2, -2, 1, -1]; it shows how far output deviates from desired value to adjust control

B. [18, 22, 19, 21]; it sums signals to increase output

C. [10, 10, 10, 10]; constant error means system is stable

D. [-2, 2, -1, 1]; error is output minus reference for feedback

Solution

1. Step 1: Calculate error signal and understand its importance

   Subtract each output value from 10: 10-8=2, 10-12=-2, 10-9=1, 10-11=-1, resulting in [2, -2, 1, -1]. The error shows how much the output deviates from desired value, guiding adjustments to improve system performance.

2. Final Answer:

   [2, -2, 1, -1]; it shows how far output deviates from desired value to adjust control -> Option A

3. Quick Check:

   Error = Reference - Output; deviation guides control [OK]

Hint: Error = desired minus actual; guides system corrections [OK]

Common Mistakes:

• Adding signals instead of subtracting
• Reversing subtraction order
• Ignoring error's role in control adjustment