Plot with linspace and for loop - what is wrong with this code?

Question

Aimee Talbot 2019-3-27

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/452868-plot-with-linspace-and-for-loop-what-is-wrong-with-this-code

回答： Catalytic 2019-3-27

c = 9000
k = 30000
m = 1100
w_n = sqrt(k/m)
z = c/(2*m*w_n)
Yo = 0.1
v = linspace(0,10);
for i = 1:length(v)
    w = 3.14*v(i);
    r = w/w_n
    X = Yo*((1-r^2)^2+(2*z*r)^2))^(1/2)
    
    f1=figure(1);
    hold on
    title('Accel vs r')
    plot(r,X);
    xlabel('r')
    ylabel('accel')
    
end
hold off

this code is supposed to create a plot of X as a function of r. V cannot exceed 10, and the variables w and r depend on this value of v.

The code is producing a blank plot when it should be some singular line.

any input would be extremeley helpful, thanks!

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Answer 1

Star Strider 2019-3-27

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/452868-plot-with-linspace-and-for-loop-what-is-wrong-with-this-code#answer_367739

在 MATLAB Online 中打开

You need to subscript ‘r’ and ‘X’ to create vectors from them, then put the plot call after the loop:

c = 9000
k = 30000
m = 1100
w_n = sqrt(k/m)
z = c/(2*m*w_n)
Yo = 0.1
v = linspace(0,10);
for i = 1:length(v)
    w = 3.14*v(i);
    r(i) = w/w_n;
    X(i) = Yo*sqrt((1-r(i)^2)^2+(2*z*r(i))^2);
end
f1=figure(1);
hold on
title('Accel vs r')
plot(r,X);
xlabel('r')
ylabel('accel')
hold off

The plot function plots lines, not individual values (unless you tell it to plot markers), so plotting individual points in each iteration will result in a blank plot.

Your code could easily be vectorised to make it more efficient, and eliminate the loop.