Advanced MATLAB test (Advanced)

Sample questions

5 sample questions from the Advanced MATLAB test, with the answers. Samples are taken out of the live test, so you will not meet these when you sit it.

1. A developer is creating a class that needs to support event handling and reference semantics. What is the correct approach to achieve this in MATLAB OOP?

   1. The class should inherit from handle to allow reference semantics and event handling.
   2. The class should be declared as a value class and use the 'dynamicprops' attribute.
   3. The class should use the 'Abstract' keyword to prevent instantiation.
   4. The class should define all methods as static to avoid inheritance.

   Answer: A. The class should inherit from handle to allow reference semantics and event handling.

   In MATLAB OOP, if a class needs to support reference semantics (so that copies point to the same object), event handling, or dynamic properties, it must inherit from the handle class. Value classes (the default) do not support these features and instead use copy-on-assignment semantics. The other options are either incorrect or not directly related to the inheritance mechanism required for reference semantics.

2. Consider the following MATLAB code snippet: `d = designfilt('multibandfir', 'bands', [0 0.2 0.3 0.5 0.6 1], 'bandtype', ['pass', 'stop', 'pass', 'stop', 'pass'], 'fs', 1000);`. Which statement accurately describes the issue with this code?

   1. The code will produce a filter bank with correct frequency responses but will not be optimised for performance.
   2. The code is correct and will produce a well-designed filter bank with accurate frequency responses.
   3. The code will fail to execute due to a syntax error in the `designfilt` function call.
   4. The code will produce a filter bank with incorrect frequency responses due to improper use of the `designfilt` function for multi-band filters.

   Answer: D. The code will produce a filter bank with incorrect frequency responses due to improper use of the `designfilt` function for multi-band filters.

   The code defines a multi-band filter bank but fails to account for the fact that `designfilt` requires specific parameters for multi-band designs, such as specifying the desired passband and stopband frequencies for each band. If not properly defined, the resulting filter bank will not produce accurate frequency responses, leading to incorrect signal processing results.

3. Which of the following statements best describes the purpose and design principles of filter banks in signal processing?

   1. Filter banks are not used in signal processing and are only relevant for mathematical analysis.
   2. Filter banks use a single high-pass filter to separate signals into two frequency bands.
   3. Filter banks are primarily used for time-domain convolution without frequency analysis.
   4. Filter banks decompose a signal into multiple frequency bands using a set of filters, typically designed with critically sampled subbands to avoid redundancy.

   Answer: D. Filter banks decompose a signal into multiple frequency bands using a set of filters, typically designed with critically sampled subbands to avoid redundancy.

   Filter banks decompose signals into multiple frequency bands using a series of filters. Critically sampled subbands ensure that the total number of samples remains constant across the decomposition, making them efficient for applications like audio and image processing. Other options are incorrect because they do not describe the primary purpose or design principles of filter banks.

4. Which of the following is the correct procedure for calculating a one-sided amplitude spectrum from the FFT output in MATLAB?

   1. Use `fftshift` to centre the zero frequency and calculate the one-sided amplitude spectrum as `abs(X(1:N/2+1))/N`, doubling all bins except DC and Nyquist.
   2. Use the full FFT output directly and double the magnitudes of all bins without modification.
   3. Use the full FFT output directly and divide by the number of samples without any modification.
   4. Use `fftshift` to centre the zero frequency and calculate the one-sided amplitude spectrum as `abs(X(1:N/2))/N` without doubling any bins.

   Answer: A. Use `fftshift` to centre the zero frequency and calculate the one-sided amplitude spectrum as `abs(X(1:N/2+1))/N`, doubling all bins except DC and Nyquist.

   The correct method for computing a one-sided amplitude spectrum involves using `fftshift` to centre the zero frequency and then taking the absolute value of the first half of the FFT output, dividing by the number of samples, and doubling the magnitudes of all bins except DC and Nyquist. Other options describe incorrect or incomplete procedures for spectral analysis.

5. You are working on a project that requires a MATLAB function to be compiled into a MEX file for faster execution. What is the correct approach to achieve this?

   1. Use MATLAB Coder to generate a MEX file from the function, then compile it using the mex command.
   2. Use the MATLAB Function Block to compile the function into a MEX file.
   3. Use the MATLAB Interpreter to compile the function into a MEX file.
   4. Use the compiler command directly on the MATLAB function file.

   Answer: A. Use MATLAB Coder to generate a MEX file from the function, then compile it using the mex command.

   MATLAB Coder is the correct tool for generating MEX files from MATLAB code. The mex command is used to compile the generated C/C++ code into a MEX file. Other options are incorrect because they either do not support MEX file generation or are unrelated to the compilation process.