Edward asked . 2021-08-25

Why is "lsim" different than Simulink's "Linear Analysis Tool"

Hi All,

I have a simple transfer function. I want to analyze its time response to a random input signal. When I use the "lsim" command (or ltiviewer), I can run a simulation. However, when I implement my transfer function in Simulink, and run the same simulation (random input) using the Linear Analysis tool, I get completely different results. Is there a fundamental difference between the two tools? It seems like Simulink and lsim/ltiview are treating my transfer function differently...

Thanks!

simulink , control system tool , lsim , ltiviewer , transfer function , linear analysis tool

Expert Answer

Prashant Kumar answered . 2024-11-24 03:32:48

Yes, several suggestions/questions.

First of all, your workflow does not quite make sense. Frequency Response Estimation capability in the Linear Analysis tool is designed for computing frequency response of nonlinear Simulink models that cannot be linearized using exact linearization due to discontinuities such as PWM or triggered subsystems. It does not make sense to use it in your case - you can if you want to, but it is meaningless.

Let me explain why. What you have is a linear system - a transfer function. There is no need to linearize Simulink model that consists only of a transfer function - you already have this transfer function to start with! Also, there is no need to use frequency response estimation. What it does is that it injects a signal into the model, logs the output, and computes the FFT of system response from the input and output signals. Again, as you already have your transfer function, there is no need to use frequency response estimation.

In your case, it seems you are trying to simulate a transfer function output to a random signal. You already know how to do it in MATLAB. To do it in Simulink, you just run the simulation, you do not need to linearize the model or use frequency response estimation. Just double check that your Random number block generates the same signal as input signal you designed in MATLAB, replace the outport block with "To workspace" block, and run the simulation. The output of the simulation will match what you got in MATLAB (you'll need to change solver's step to be fixed step with the same sampling time you use in MATLAB code).

Now, if you really want to know why the time response you are getting in Frequency Response Estimation tool is different, read on.

1. First of all, when you use frequency response estimation, and generate an excitation signal, this excitation signal is added to the signal you already have in your Simulink model . In your case, this means that the input to your Simulink model, when you run frequency response estimation, will be the random signal you specify in frequency response estimation tool added to the output of Random Number block you have in your model. So what the model sees is a different input signal than what you have in your MATLAB code.

2. Even if you replace Random Number block with zero constant (so when you run frequency response estimation, model will only see the excitation signal you define in Frequency Response Estimation tool), (actually, a better way is to tell the tool to hold the output of this block constant, using BlocksToHoldConstant option ) you need to be careful with this random signal you specify in Frequency Response Tool. To get the same results as what you got with MATLAB code, that random signal from Frequency Response Estimation tool needs to match your input signal in MATLAB exactly. What you use in MATLAB is a random number, normal distribution with standard deviation of 1. The random signal in Frequency Response Estimation is a uniform random number spanning from 0 to Amplitude, so it will be a different signal than what you have in MATLAB, and therefore, you will get a different output.

Not satisfied with the answer ?? ASK NOW

Recent Matlab Projects

Classification of Covid and Non-Covid Lungs CT-Scan using Deep Learning with MATLAB

Matlab simulation on Wind Energy system

Frequently Asked Questions

MATLAB offers tools for real-time AI applications, including Simulink for modeling and simulation. It can be used for developing algorithms and control systems for autonomous vehicles, robots, and other real-time AI systems.

MATLAB Online™ provides access to MATLAB® from your web browser. With MATLAB Online, your files are stored on MATLAB Drive™ and are available wherever you go. MATLAB Drive Connector synchronizes your files between your computers and MATLAB Online, providing offline access and eliminating the need to manually upload or download files. You can also run your files from the convenience of your smartphone or tablet by connecting to MathWorks® Cloud through the MATLAB Mobile™ app.

Yes, MATLAB provides tools and frameworks for deep learning, including the Deep Learning Toolbox. You can use MATLAB for tasks like building and training neural networks, image classification, and natural language processing.

MATLAB and Python are both popular choices for AI development. MATLAB is known for its ease of use in mathematical computations and its extensive toolbox for AI and machine learning. Python, on the other hand, has a vast ecosystem of libraries like TensorFlow and PyTorch. The choice depends on your preferences and project requirements.

You can find support, discussion forums, and a community of MATLAB users on the MATLAB website, Matlansolutions forums, and other AI-related online communities. Remember that MATLAB's capabilities in AI and machine learning continue to evolve, so staying updated with the latest features and resources is essential for effective AI development using MATLAB.

Without any hesitation the answer to this question is NO. The service we offer is 100% legal, legitimate and won't make you a cheater. Read and discover exactly what an essay writing service is and how when used correctly, is a valuable teaching aid and no more akin to cheating than a tutor's 'model essay' or the many published essay guides available from your local book shop. You should use the work as a reference and should not hand over the exact copy of it.