Plotting sequences over intervals

Question

Connor Wright 2020-11-13

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/646803-plotting-sequences-over-intervals

回答： Md. Monirul Islam 2022-10-30

采纳的回答： Jon

Hello,

How would I go about plotting a seqeunce over the below intervals?

A) 𝑥(𝑛) = 2𝛿(𝑛 + 1)− 𝛿(𝑛 −6), −10 ≤ 𝑛 ≤ 10.

B) 𝑥(𝑛) = {… , 5, 4, 3, 2, 1, 5, 4, 3, 2, 1, 5, 4, 3, 2, 1, … }; −20 ≤ 𝑛 ≤ 12.

Thanks

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Jon 2020-11-13

在 MATLAB Online 中打开

Sorry you haven't been able to get any help. Maybe I can try to get you started.

Let's start with problem a.

First note that the unit sample function, delta(arg) has a value of 1 when arg = 0 and otherwise is zero. So for example delta(0) = 1 delta(-3) = 0, delta(4) = 0 etc and delta(n) = 1 when n = 0 and delta(n) = 0 when n is not equal zero. You can also shift the argument relative to n, so delta(n + 1) = 1 when n = - 1 (because the argument n+1 =0 when n = -1) and so on. So now look at your series and start plugging in values for n starting at n = -10. x(-10) = 2*delta(-10+1) - delta(-10 -6) So x(n) = 2*delta(-9) -delta(-16) ,x(n) = 2*0 -0 x(n) = 0 Now repeat for n = -9

x(-9) = 2*delta(-8) - delta(-15) , x(-9) = 0 and so on. Some terms will finally be non zero

Now think about how you would automate this is MATLAB, you could use a for loop like this

n = -10:10
x = zeros(length(n),1) % preallocate array of zeros to hold result
for k = 1:length(n)
    arg1 = n(k) + 1
    if arg1 == 0
        delta1 = 1
    else
        delta1 = 0 % 2*0
    end
    
    arg2 = n(k) - 6
    if arg2 == 0
        delta2 = 1
    else
        delta2 = 0
    end
    % compute x for this element in seqence
    x(k) = 2*delta1 - delta2
end
% plot result
stem(n,x)

But this isn't very good coding practice because we shouldn't cut and paste the same code twice. Otherwise you might fix something in the first part and forget to fix it in other, plus it has lots of extra lines to read. Instead you could define a unit sample function and do it like this

n = -10:10
x = zeros(length(n),1) % preallocate array of zeros to hold result
for k = 1:length(n)
    % evaluate x(n)
    x(k) = 2*usmpl(n(k)+ 1) - usmpl(n(k)-6);
end
% plot result
stem(n,x)
% define helper function
function delta = usmpl(n)
% define unit sample function
if n == 1
    delta = 1
else
    delta = 0
end
end

Connor Wright 2020-11-16

Thanks for the help, just been looking through and doing some playing around with the code you have provided, I have run into an issue with usmpl repeatedly. MatLab throws the error, Unrecognized function or variable 'usmp1'.

Is this part of an add in package?

Jon 2020-11-19

I define it as a helper function in my script above

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Answer 1

Jon 2020-11-19

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/646803-plotting-sequences-over-intervals#answer_550183

在 MATLAB Online 中打开

You could do it like this

n = -10:10
x = zeros(length(n),1) % preallocate array of zeros to hold result
for k = 1:length(n)
    % evaluate x(n)
    x(k) = 2*usmpl(n(k)+ 1) - usmpl(n(k)-6);
end
% plot result
stem(n,x)
% define helper function
function delta = usmpl(n)
% define unit sample function
if n == 1
    delta = 1
else
    delta = 0
end
end

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Connor Wright 2020-11-19

I'm studying Electronic and Electrical Engineering, I am a fabricator, machinist, welder by trade and blacksmith by hobby who doesn't have any formal Mathematics qualification. So with that said you can belive I have many questions 😂

Jon 2020-11-20

Great that your working on developing your skills, sounds like you have lots of talents, definitely post some new questions if you have more MATLAB questions. I've learned a lot from this site, there are a lot of knowledgeable people answering questions. By the way, you may already be beyond this, but if not the MATLAB On Ramp course is good for getting a quick start https://www.mathworks.com/learn/tutorials/matlab-onramp.html

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Answer 2

SaiDileep Kola 2020-11-16

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/646803-plotting-sequences-over-intervals#answer_545883

Hi Connor,

Start by copying complete code provided by Jon and usmpl is just a local function created to use. Don't use usmpl in the terminal without defining, that will solve your issue.

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Jon 2020-11-16

Hi thanks to SaiDileep Kola for helping Connor with this.

I'm glad you finally got it running without errors. You can run the code as a live script, or just as a plain script (just save it as a .m file.

Note I tried to make the example self contained by including the function definition for the unit sample function (usmpl) inside of the script. If you want to make it available to other scripts, or at the command line then you can cut and paste that function definition into it's own m file. As long as the location for that file is on the MATLAB search path it will then be available to use on the command line or within another script or function. Note if it is saved in the folder from which you are currently running MATLAB it will already be on the path.

When you say the graph does not look as you expect, maybe you can be more specific. Note I just quickly provided the code to give you an example to gety you started on how to think about this going about how to do this. I didn't carefully check to see that the answer was correct. You should check the details of the code to make sure that the calculations make sense to you, and possible correct any errors if you find them.

Connor Wright 2020-11-19

I understand completely Jon, if your answer was posted on the answers I would of accepted yours. I do truly appreciate your help however, after a little digging around I managed to sort the graph output out turns out that all that needed to be done was to change the delta value to 2*1.

Jon 2020-11-19