How to make 3D-line plots (Sine Wave)?

Question

Hamid Kilic 2019-11-21

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https://ww2.mathworks.cn/matlabcentral/answers/492370-how-to-make-3d-line-plots-sine-wave

评论： Adam Danz 2019-11-21

Hi everybody, I am new to MATLAB and I need a help with this problem.

Plot a series of sine functions which are phase shifted by pi/10 and whose amplitudes are increased by 0.2. Final result is going to be like this. I tried bunch of methods but I couldn't get it. Thanks in advance.

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Adam Danz 2019-11-21

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I just looked at your code more carefully (previously I just looked at the figure it produced). There are some problems that I'll address individually.

1) I recommend not using this style of loops: for a = 1:0.2:4

Instead, define 'a' as a vector and use integers as your loop variable. That would look something like this, below. The following tips assumes you've made this change.

a = 1:0.2:4 ;
for i = 1:numel(a)
    %[code omitted]
    y = a(i) .*sin(t + phase);
    %[code omitted]
end

2) In your loop you are defining phase as 0: phase = 0 so there will be no phase shifts. Move the phase outside of the loop and define it as a vector that has 1 value for each iteration of the loop.

3) Most importantly, you aren't saving the y-values within the loop! They are being overwritten on each iteration. disp(y) only displays the y-values in the command window. That slows down the code and should be removed. To save the y values on each iterations,

y = nan(numel(t), numel(a)); % each column will contain data from 1 iteration
for i = 1:numel(a)
     %[code omitted]
     y(:,i) = a(i) .*sin(t + phase);  %store in column i
     %[code omitted]
end

Those are the next steps to take. Use those tips to apply additional changes you'll need to make to get the script working. Examine each variable. Is it the size that you are expecting? Does it have values that make sense? If you get stuck again, follow up with another comment but try to get a few steps further than the advice already provided.

Hamid Kilic 2019-11-21

Thanks, you have given me so many useful tips.

Adam Danz 2019-11-21

Glad I could help - I think you would have gotten there on your own which is a great learning process. Take time to understand each line of the answer that Star Strider gave to you so you can own the assignment and understand why it works.

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Answer 1

Star Strider 2019-11-21

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https://ww2.mathworks.cn/matlabcentral/answers/492370-how-to-make-3d-line-plots-sine-wave#answer_402627

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With three small changes to your code, it works:

t = 0:0.01:5*pi;
z = 0:pi/12:2*pi;
phase = 0;                                          % Initiliise Outside The Loop
a = 1:0.2:4;                                        % Assign Outside The Loop
 for k = 1:numel(a)
        y(k,:) = a(k)*sin(t + phase);
        phase = phase + pi/10;
%         disp(y)     
 end
axes()
hold on
for i = 1:numel(z)
    plot3(t,z(i)*ones(size(t)),y);
end

The changes are with respect to ‘phi’ and ‘phase’, and adding the ‘k’ loop counter and subscript.

My solution:

t = linspace(0, 4*pi);
a = (1:25);
sinmtx = 0.2*a(:).*sin(t + a(:)*pi/10);
figure
plot3(t, a(:)*ones(size(t)), sinmtx)
grid on
view(35,45)

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Answer 2

Adam Danz 2019-11-21

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https://ww2.mathworks.cn/matlabcentral/answers/492370-how-to-make-3d-line-plots-sine-wave#answer_402608

编辑：Adam Danz 2019-11-21

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Since this seems like homework, my solution below shows how to produce the figure but you'll need to adapt it to comply with the requirements of the assignment.

t = 0:0.01:5*pi;
y = sin(t);
z = 0:pi/12:2*pi;
clf()
axes()
hold on
for i = 1:numel(z)
    plot3(t,z(i)*ones(size(t)),y);
end
grid on
xlabel('t')
ylabel('o.5 pi')  % Replace with ylabel(['0.5',char(960)]) for pi symbol
zlabel('sin(t)')
view(12.6, 27.6)