Why does my fplot output a plot filled with colored horizontal lines?

Question

Shane Palmer 2019-11-12

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/490564-why-does-my-fplot-output-a-plot-filled-with-colored-horizontal-lines

评论： Walter Roberson 2019-11-12

fplot.JPG

I am trying to run an fplot command and the resulting plot does not give me my expected output. The fplot is full of horizontal colored lines that I have no idea how to eliminate or to troubleshoot.

See attached screenshot.

omega_b=1800;
X=-4/(1800^2);
m=0.003;
k=10720;
c=0.01;
omega_n=sqrt(k/m);
zeta=c/(2*m*omega_n);
r=omega_b/omega_n;
theta_1=atan((2*zeta*omega_n*omega_b)/(omega_n^2-omega_b^2));
theta_2=atan(omega_n/(2*zeta*omega_b));
y=omega_n*X*((omega_n^2+(2*zeta*omega_b)^2)/((omega_n^2-omega_b^2)^2+(2*zeta*omega_n*omega_b)^2))^0.5*cos(omega_b*t-theta_1-theta_2)
fplot(y,[0 6*pi()])

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Answer 1

Walter Roberson 2019-11-12

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https://ww2.mathworks.cn/matlabcentral/answers/490564-why-does-my-fplot-output-a-plot-filled-with-colored-horizontal-lines#answer_401044

Your t is numeric, a 1 x 593 vector. Your y is then a 1 x 593 vector, with no symbolic variables. fplot() is then plotting those 593 different constant values over a range of x (which has no effect because the values are constant.)

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Shane Palmer 2019-11-12

Hello Walter,

Thank you for your quick response, I am not understanding how to properly define my function to plot then. I want to plot a function of t, but I dont want to define values of t until I use the "fplot" command. What would be the best method to do this?

Thanks alot!