Asked to plot using vectors of unequal sizes

Question

B.M. 2014-2-9

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https://ww2.mathworks.cn/matlabcentral/answers/115447-asked-to-plot-using-vectors-of-unequal-sizes

评论： B.M. 2014-2-10

I am working on the following problem:

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We wish to examine the motion of a damped harmonic oscillator. The small amplitude oscillation of a unit mass attached to a spring is given by the formula y = e−(R/2)t sin(ω1t ), where ω2 1 = ω2 o − R2/4 is the square of the natural frequency of the oscillation with damping (i.e., with resistance to motion); ω2 o = k is the square of the natural frequency of undamped oscillation; k is the spring constant; and R is the damping coefficient. Consider k = 1 and vary R from 0 to 2 in increments of 0.5. Plot y versus t for t from 0 to 10 in increments of 0.1.

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My main problem with this problem is that I am told to evaluate y for R=0:0.5:2, but plot over the range of t=0:0.1:10. How can this work, if y is 1x5 and t is 1x101?

Here is my code, minus the line for t, which I make the same as R to get y, but then try to change when going to plot (doesn't work):

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k= 1; %spring constant

R=[0:0.5:2]; %damping coeff

w0=sqrt(k);

w1=sqrt((w0^2)-R.^2/4);

y=exp(-(R./2).*t).*(sin(w1.*t));

plot(t,y)

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Answer 1

Mischa Kim 2014-2-10

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https://ww2.mathworks.cn/matlabcentral/answers/115447-asked-to-plot-using-vectors-of-unequal-sizes#answer_123822

编辑：Mischa Kim 2014-2-10

在 MATLAB Online 中打开

B.M., simply compute y in a for-loop and plot the results in the same figure using hold all. You also might want to include markers and a legend for readability. Use colors and markers to specify the color and marker type for each of the plots.

k  = 1; %spring constant
R  = 0:0.5:2; %damping coeff
t  = 0:0.1:10;
w0 = sqrt(k);
w1 = sqrt((w0^2)-R.^2/4);
figure
hold all; grid; box
colors  = 'krbcy';
markers = 'x+*.o';
for ii = 1:length(R)
    y(ii,:) = exp(-(R(ii)/2).*t).*(sin(w1(ii)*t));
    plot(t,y(ii,:),[markers(ii) colors(ii)]);
end
xlabel('t in s')
ylabel('y in TBD')
legend('R0','R1','R2','R3','R4')

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B.M. 2014-2-10

Thanks Mischa. The book I'm using hasn't gone into much detail about plotting yet so I figured there was some more complicated way to do it...just wish I could figure out what they were expecting given the simple discussion so far.

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