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180 - 199 of 440

Mishal Mohanlal
Last activity am 17 Nov. 2023

Compression only spring mass system

Hi Guys

Posting this based on a thought I had, so I don't really ahve any code however I would like to know if the thought process is correct and/or relatively accurate.

Consider a simple spring mass system which only allows compression on the spring however when there is tension the mass should move without the effect of the spring distrupting it, thus the mass is just thrown vertically upwards.

The idea which I came up with for such a system is to have two sets of dfferential equations, one which represents the spring system and another which presents a mass in motion without the effects of the spring.

Please refer to the below basic outline of the code which I am proposing. I believe that this may produce relatively decent results. The code essentially checks if there is tension in the system if there is it then takes the last values from the spring mass differential equation and uses it as initial conditions for the differential equation with the mass moving wothout the effects of the spring, this process works in reverse also. The error which would exist is that the initial conditions applied to the system would include effects of the spring. Would there be a better way to code such behaviour?

function xp = statespace(t,x,f,c,k,m)
    if (k*x(1)) positive #implying tension
      **Use last time step as initial conditions**
      **differential equation of a mass moving""
    end
    if x(1) negative #implying that the mass in now moving down therefore compression in spring
      **Use last time step as initial conditions**
      **differential equation for a spring mass system**
    end
end

Ideas

Martin Ryba
Last activity am 12 Dez. 2023

AWGN SNR calibration for band limited signals

Seeing a colleague make this mistake (one I've had to fix multiple times in other's work too) makes me want to ask the community: would you like the awgn() function/blocks to give the option for creating a SNR at the bandwidth of the signal? Your typical flow is something like this:

Create a signal, usually at some nominal upsampling factor (e.g., 4) such that it's now nicely over sampled, especially if you're using a RRC or similar pulse shaping filter.
Potentially add a frequency offset (which might make the sample frequency even higher)
Add AWGN channel model for a desired SNR
Put this into your detector/receiver model

The problem is, when someone says, "I'm detecting XYZ at foo SNR," it should not magically improve as a function of the oversample. The problem isn't that awgn() generates white noise, that's what it's supposed to do and the typical receiver has noise across the entire band. The problem is that SNR is most properly defined as the signal power over the noise power spectral density times the signal's noise equivalent bandwidth. Now I looked and there's no handy function for computing NEBW for an input signal (there's just a function for assessing analysis windows). In practice it can get a bit tricky. The occupied bandwidth or HPBW are often close enough to the NEBW, we're usually not haggling over hundredths of a dB. So, in my not so humble opinion, the "measured" flag for awgn() should give an option for bandwidth matching or at least document the behavior better in the help page. All too often I'm seeing 3-6 (or worse) dB errors because people aren't taking the signal's bandwidth into account.

General

LAWAN HARUNA
Last activity am 6 Nov. 2023

mentorship

good afternoon everyone my name is Dundu lawan haruna ,i'm a final year student at the department of computer engineering ABU Zaria, Nigerian , and i wanted to do my final year project based on computer vision : project topic , designing an eye glasses to help those people with visual imparement to be able to navigate enviroment efficiently , that's why i need a support from you guys ,all advised are highly well come , thank you for your support.

Highlights

Chen Lin
Last activity am 10 Nov. 2023

Join Community Contest 2023: Unleash Your Creativity with MATLAB Animations!

You are invited to join our 2023 community contest – MATLAB Flipbook Mini Hack! This year’s contest revolves around creating interesting animations using MATLAB.

Whether you are a seasoned MATLAB user or just getting started, this contest offers a fantastic opportunity to showcase your skills, learn from others, and engage with the vibrant MATLAB Central community.

Timeframe

This contest runs for 4 weeks from Nov. 6th to Dec. 3rd.

How to play

Create a new animation or remix an existing one with up to 2,000 characters of code.
Simply vote on the animations you love!

Prizes

You will have opportunities to win compelling prizes, including Amazon gift cards, MathWorks T-shirts, and virtual badges. We will give out both weekly prizes and grand prizes.

Check out the gallery and vote on the animations you like.

The MATLAB Central Community team

Fun

Image Analyst
Last activity am 31 Okt. 2023

BATLAB

Just in time for Halloween.

meme

Fun

Chen Lin
Last activity am 12 Mär. 2024

What costume are you going to wear for Halloween?

Share your fun photos in the comments!

halloween

Highlights

Adam Danz
Last activity am 9 Dez. 2023

Why do you save figure (.fig) files?

I rarely/never save .fig files

47%

Continue working on it later

16%

Archive for future reference

23%

Share within my organization

10%

Share outside my organization

Other (please leave a comment)

2097 Stimmen

Ideas

Julian
Last activity am 5 Feb. 2024

Naming x-values in bar(x,y)

I know the latest version of MATLAB R2023b has this feature already, put it should be added to R2023a as well because of its simplicity and convenience.

Basically, I want to make a bar graph that lets me name each column in a basic bar graph:

y=[100 99 100 200 200 300 500 800 1000];

x=["0-4" "5-17" "18-29" "30-39" "40-49" "50-64" "65-74" "75-84" "85+"];

bar(x,y)

However, in R2023a, this isn't a feature. I think it should be added because it helps to present data and ideas more clearly and professionally, which is the purpose of a graph to begin with.

General

Kilsu Kim
Last activity am 19 Okt. 2023

Just for Fun and Curiosity: Guess the MATLAB Compile Threshold on Windows

Recently, I came across a post about the JIT compiler on this Korean blog. In the post. The writer discussed the concept of the "Compile Threshold" and how it is calculated.

"The JVM accumulates the number of calls for each method called and compiles when the number exceeds a certain number. In other words, there is a standard for checking how often it is called and then deciding, 'It is time to compile.' This standard is called the compilation threshold. But what is this and why should it be used as a standard?"

The concept of the "Compile Threshold," as used above, seems to be more commonly associated with Tracing just-in-time compilation.

The writer used the simple Java code below to calculate the threshold.

for (int i = 0; i < 500; ++i) {
  long startTime = System.nanoTime();
  for (int j = 0; j < 1000; ++j) {
 	new Object();
  }
  long endTime = System.nanoTime();
  System.out.printf("%d\t%d\n", i, endTime - startTime);
}

Since the MATLAB execution engine uses JIT compilation, I just wanted to perform the same experiment that the writer did.

I experimented using simple codes based on the code in the blog. I iterated a function 500 time using for-loop and calculated the execution time for each iteration using tic and toc. Then I plotted the execution time for each loop as blow. First five execution times are much higher than followings (10 times!) The test is very rough so I am not sure that I can conclude "MATLAB has Compile Threshold and it is 5!" but this value is actually correct ;-)

t0 = 0;
tfinal = 10;
y0 = [20;20];
timeToRun = zeros(500,1);
for i = 1:500
    tStart = tic;
    [preypeaks,predatorpeaks] = solvelotka(t0, tfinal, y0);
    tEnd = toc(tStart);
    timeToRun(i) = tEnd;
end

General

Toshiaki Takeuchi
Last activity am 23 Okt. 2023

Do you use VS Code for writing MATLAB Code?

VS Code Extension for MATLAB was introduced back in April and has been downloaded 75K times since. Do people here use VS Code for writing MATLAB code?

vs code

Ideas

Matt J
Last activity am 1 Mär. 2024

Implicit expansion for CAT()

Would it be a good thing to have implicit expansion enabled for cat(), horzcat(), vertcat()? There are often situations where I would like to be able to do things like this:

 x=[10;20;30;40];
 y=[11;12;13;14];
 z=cat(3, 0,1,2);
 
 C=[x,y,z]
 

with the result,