Why are the lines not showing up on my graphs?

Question

Anna Zito 2020-5-25

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/532513-why-are-the-lines-not-showing-up-on-my-graphs

评论： Star Strider 2020-5-25

采纳的回答： Star Strider

g=9.81;

Ta=10;

mA=20;

for i=1:100

M=(i-1)*(30/99);

mB=4.05;

mC=M;

mD=M;

JC=0.005*M;

JD=JC;

JA=0.8055;

A=[mA 0 -1 1 0 0 0; (5*JA) 0 0.2 0 0 0 0; (10*JC) 0 0 -0.1 0 0.1 0; 0 mD 0 0 -1 -1 -1; 0 (10*JD) 0 0 0 -0.1 0.1; 0 mB 0 0 -1 0 0; -0.5 1 0 0 0 0 0];

B=[0; Ta; 0; (-mD*g); 0; (-mB*g); 0];

x=inv(A)*B;

aA(i)=x(1); aB(i)=x(2); FA(i)=x(3); TA(i)=x(4); TB(i)=x(5); TC(i)=x(6); TD(i)=x(7);

end

Mvector=linspace(0,30,100);

plot(Mvector, aA(i),'g',Mvector,aB(i),'b-.');

title('Acceleration');

legend('Disk A','Mass B');

xlabel('M (kg)');

ylabel('Acceleration (m/s^2)');

pause

plot(Mvector,aA(i),'g',Mvector,aB(i),'b-.');

title('Acceleration');

legend('Disk A','Mass M');

xlabel('M (kg)');

ylabel('acceleration (m/s^2)');

pause

plot(Mvector, FA(i),'k');

title('Plot 3');

xlabel('M (kg)');

ylabel('FA (N)');

pause

plot(Mvector,TA(i),'g',Mvector,TB(i),'b-.');

title('Plot 4');

legend('Cable A','Cable B');

xlabel('M (kg)');

ylabel('Tension (N))');

pause

plot(Mvector,TA(i),'g',Mvector,TC(i),'b:',Mvector,TD(i),'r-.');

title('Plot 5');

legend('Cable A','Cable C','Cable D');

xlabel('M (kg)');

ylabel('Tension (N)');

pause

plot(Mvector,FA(i)/(mA*g),'k');

title('Plot 6');

xlabel('M (kg)');

ylabel('mu');

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Answer 1

Star Strider 2020-5-25

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/532513-why-are-the-lines-not-showing-up-on-my-graphs#answer_437953

在 MATLAB Online 中打开

You are only plotting one point (that being the last point) and it is not possible to plot lines with only one point.

Try this:

Mvector=linspace(0,30,100);
figure
plot(Mvector, aA,'g',Mvector,aB,'b-.');
title('Acceleration');
legend('Disk A','Mass B');
xlabel('M (kg)');
ylabel('Acceleration (m/s^2)');
% pause
figure
plot(Mvector,aA,'g',Mvector,aB,'b-.');
title('Acceleration');
legend('Disk A','Mass M');
xlabel('M (kg)');
ylabel('acceleration (m/s^2)');
% pause
figure
plot(Mvector, FA,'k');
title('Plot 3');
xlabel('M (kg)');
ylabel('FA (N)');
% pause
figure
plot(Mvector,TA,'g',Mvector,TB,'b-.');
title('Plot 4');
legend('Cable A','Cable B');
xlabel('M (kg)');
ylabel('Tension (N))');
% pause
figure
plot(Mvector,TA,'g',Mvector,TC,'b:',Mvector,TD(i),'r-.');
title('Plot 5');
legend('Cable A','Cable C','Cable D');
xlabel('M (kg)');
ylabel('Tension (N)');
% pause
figure
plot(Mvector,FA/(mA*g),'k');
title('Plot 6');
xlabel('M (kg)');
ylabel('mu');

Also, you were overplotting each new plot on the previous one, erasing the previous one. Since it appears you want them on separate figures, this slightly revised code does that. If you want to plot all of them on the sane axes, use the hold function.

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Star Strider 2020-5-25

在 MATLAB Online 中打开

My pleasure!

I am not certain what you are referring to. The code in my Answer worked with the code in your original Question. The full code with your original loop and my revisions in the plotting section is now:

g=9.81;
Ta=10;
mA=20;
for i=1:100
    M=(i-1)*(30/99);
    mB=4.05;
    mC=M;
    mD=M;
    JC=0.005*M;
    JD=JC;
    JA=0.8055;
  
A=[mA 0 -1 1 0 0 0; (5*JA) 0 0.2 0 0 0 0; (10*JC) 0 0 -0.1 0 0.1 0; 0 mD 0 0 -1 -1 -1; 0 (10*JD) 0 0 0 -0.1 0.1; 0 mB 0 0 -1 0 0; -0.5 1 0 0 0 0 0];
B=[0; Ta; 0; (-mD*g); 0; (-mB*g); 0];
x=A\B;
aA(i)=x(1); aB(i)=x(2); FA(i)=x(3); TA(i)=x(4); TB(i)=x(5); TC(i)=x(6); TD(i)=x(7);
end
Mvector=linspace(0,30,100);
figure
plot(Mvector, aA,'g',Mvector,aB,'b-.');
title('Acceleration');
legend('Disk A','Mass B');
xlabel('M (kg)');
ylabel('Acceleration (m/s^2)');
% pause
figure
plot(Mvector,aA,'g',Mvector,aB,'b-.');
title('Acceleration');
legend('Disk A','Mass M');
xlabel('M (kg)');
ylabel('acceleration (m/s^2)');
% pause
figure
plot(Mvector, FA,'k');
title('Plot 3');
xlabel('M (kg)');
ylabel('FA (N)');
% pause
figure
plot(Mvector,TA,'g',Mvector,TB,'b-.');
title('Plot 4');
legend('Cable A','Cable B');
xlabel('M (kg)');
ylabel('Tension (N))');
% pause
figure
plot(Mvector,TA,'g',Mvector,TC,'b:',Mvector,TD(i),'r-.');
title('Plot 5');
legend('Cable A','Cable C','Cable D');
xlabel('M (kg)');
ylabel('Tension (N)');
% pause
figure
plot(Mvector,FA/(mA*g),'k');
title('Plot 6');
xlabel('M (kg)');
ylabel('mu');

I am not certain what you are doing with the new vectors. You likely have to make all of them conform to the same length. This is easier using linspace than using the colon operator.

Without your code, I can only guess as to what the problems is. One guess is that you are starting the ‘i’ loop at 0 rather than 1.

One way to make all the vectors have lengths of 100 and still have ‘i’ go from 0 to 100 is:

g=9.81;
Ta=10;
mA=20;
iv = linspace(0, 100);
for k=1:numel(iv)
    i = iv(k);
    M=(i-1)*(30/99);
    mB=4.05;
    mC=M;
    mD=M;
    JC=0.005*M;
    JD=JC;
    JA=0.8055;
  
A=[mA 0 -1 1 0 0 0; (5*JA) 0 0.2 0 0 0 0; (10*JC) 0 0 -0.1 0 0.1 0; 0 mD 0 0 -1 -1 -1; 0 (10*JD) 0 0 0 -0.1 0.1; 0 mB 0 0 -1 0 0; -0.5 1 0 0 0 0 0];
B=[0; Ta; 0; (-mD*g); 0; (-mB*g); 0];
x=A\B;
aA(k)=x(1); aB(k)=x(2); FA(k)=x(3); TA(k)=x(4); TB(k)=x(5); TC(k)=x(6); TD(k)=x(7);
end

That (with the plotting code I previously posted) runs without error.

If I guessed incorrectly, please explain in more detail how you are getting vectors with lengths of 101.

Anna Zito 2020-5-25

编辑：Image Analyst 2020-5-25

在 MATLAB Online 中打开

Here is the new code I just attempted to run:

g=9.81;
Ta=10;
mA=20;
iv = linspace(0, 100);
for k=1:numel(iv)
    i = iv(k);
    M=(i-1)*(30/99);
    mB=4.05;
    mC=M;
    mD=M;
    JC=0.005*M;
    JD=JC;
    JA=0.8055;
  
A=[mA 0 -1 1 0 0 0; (5*JA) 0 0.2 0 0 0 0; (10*JC) 0 0 -0.1 0 0.1 0; 0 mD 0 0 -1 -1 -1; 0 (10*JD) 0 0 0 -0.1 0.1; 0 mB 0 0 -1 0 0; -0.5 1 0 0 0 0 0];
B=[0; Ta; 0; (-mD*g); 0; (-mB*g); 0];
x=A\B;
aA(k)=x(1); aB(k)=x(2); FA(k)=x(3); TA(k)=x(4); TB(k)=x(5); TC(k)=x(6); TD(k)=x(7);
end
Mvector=linspace(0,30,100);
figure
plot(Mvector, aA,'g',Mvector,aB,'b-.');
title('Acceleration');
legend('Disk A','Mass B');
xlabel('M (kg)');
ylabel('Acceleration (m/s^2)');
% pause
figure
plot(Mvector,aA,'g',Mvector,aB,'b-.');
title('Acceleration');
legend('Disk A','Mass M');
xlabel('M (kg)');
ylabel('acceleration (m/s^2)');
% pause
figure
plot(Mvector, FA,'k');
title('Plot 3');
xlabel('M (kg)');
ylabel('FA (N)');
% pause
figure
plot(Mvector,TA,'g',Mvector,TB,'b-.');
title('Plot 4');
legend('Cable A','Cable B');
xlabel('M (kg)');
ylabel('Tension (N))');
% pause
figure
plot(Mvector,TA,'g',Mvector,TC,'b:',Mvector,TD(i),'r-.');
title('Plot 5');
legend('Cable A','Cable C','Cable D');
xlabel('M (kg)');
ylabel('Tension (N)');
% pause
figure
plot(Mvector,FA/(mA*g),'k');
title('Plot 6');
xlabel('M (kg)');
ylabel('mu');

Here is the error message:

Error using plot

Vectors must be the same length.

Error in Untitled3 (line 22)

plot(Mvector, aA,'g',Mvector,aB,'b-.');

The workspace indicates that aA, aB, FA, TA, TB, TC, and TD are all 1x101, while iv and Mvector are 1x100.

I'm sorry i have so many questions.. I am very new to matlab lol!

Anna Zito 2020-5-25

That worked!!! Thank you so much! Youre amazing!!!!!!

Star Strider 2020-5-25

As always, my pleasure! Thank you!

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Why are the lines not showing up on my graphs?

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