Why are the lines not showing up on my graphs?

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');

Answer 1

[Star Strider]

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.

[Anna Zito]

Thank you!! It is telling me now that i can not plot the figure because the vectors are not the same length. I want them to be 1x100, but all of the variables in the for loop are 1x101. How can i fix this? Mvector is 1x100.

[Star Strider]

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]

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!

[Star Strider]

I just now ran the code you posted in your last Comment, and it ran without error.

‘The workspace indicates that aA, aB, FA, TA, TB, TC, and TD are all 1x101’

In my workspace, they are all (1x100).

There is something else in your code that you are not posting that must be causing the error.

Did you preallocate them before the code you posted to create them as (1x101)? That is the only thing I can think of that would cause that error. My code would not overwrite that preallocation.

Add this clear call just before you define ‘g’ and the rest, and see if that solves the problem:

clear aA aB FA TA TB TC TD

If you are preallocating them as (1x101) and that is causing the problem, clearing them just before the code I posted should solve it.

[Image Analyst]

Same as Star -- all 1x100 and I get 6 plots with no errors. Try putting this at the beginning of your script

clear all;

or

clearvars;

[Anna Zito]

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

[Star Strider]

As always, my pleasure! Thank you!