Why is an extra line being plotted?

Hello,

I have been trying to display the deflection and displacement of beams within a building. Currently, I am having an issue from within my loop which plots the displacement of each floor.

As you can see from the plot below, I have a red horizontal line from (0,0) to(2,0). Why is this? I think I have done something wrong in my "Displacement" loop but I am not sure

numFlr=2
Phi_EigVec=[1 3;2 -3;]

y1=zeros(numFlr,1);
y2=zeros(numFlr,1);
x1=zeros(numFlr,1);
x2=Phi_EigVec(:,1);

%Displacement
hold on
for i=1:numFlr
    y1(i)=i
    y2(i)=i
A = [x1(:) x2(:)]; B = [y1(:) y2(:)];
plot(A.',B.','r')
end

%Beam Deflection
AZero=[0]
BZero=[0]
AEven=A(:,2:2:end);
BEven=B(:,2:2:end);
AFull=[AZero,AEven']
BFull=[BZero,BEven']
plot(AFull.',BFull.','g')

%Vertical Line
y=numFlr
line([0,0],[0,y])

%Axis
axis([-5 5 -1 5])

[Adam Danz]

Look at your A/B variables and recall that a line will be drawn for each column of inputs.

[Joshua Tsui]

Thanks Adam. I thought I was creating coordinates this way. Would you mind giving me some more insight as to how I can improve? I think my understanding is a bit flawed.

[Adam Danz]

You just need to move the two commented lines outside of the loop. Alan Stevens's answer does this (though, no need for the 2nd "hold on").

hold on
for i=1:numFlr
    y1(i)=i
    y2(i)=i
% A = [x1(:) x2(:)]; B = [y1(:) y2(:)];
% plot(A.',B.','r')
end

UPDATE

Actually, you don't need the loop at all,

y1 = 1:numFlr; 
y2 = y1; 
A = [x1(:) x2(:)]; B = [y1(:) y2(:)];
hold on
plot(A.',B.','r')

Answer 1

[Alan Stevens]

More like this, I think:

numFlr=2;
Phi_EigVec=[1 3;2 -3;];

y1=zeros(numFlr,1);
y2=zeros(numFlr,1);
x1=zeros(numFlr,1);
x2=Phi_EigVec(:,1);

%Displacement
hold on
for i=1:numFlr
    y1(i)=i;
    y2(i)=i;
end
A = [x1(:) x2(:)]; B = [y1(:) y2(:)];
plot(A(1,:),B(1,:),'r',A(2,:),B(2,:),'r')
hold on

%Beam Deflection
AZero=[0];
BZero=[0];
AEven=A(:,2:2:end);
BEven=B(:,2:2:end);
AFull=[AZero,AEven'];
BFull=[BZero,BEven'];
plot(AFull.',BFull.','g')

%Vertical Line
y=numFlr;
line([0,0],[0,y])

%Axis
axis([-5 5 -1 5])

[Joshua Tsui]

Thanks. This answer works for 2 floors but not 3 or more.

For example:

numFlr=3

Phi_EigVec=[1 3;2 -3;3 4;];

A red line at the top is missing.

Is there a way to put this into a loop rather than mentioning the specific lines?

[Alan Stevens]

Extend the plot command

plot(A(1,:),B(1,:),'r',A(2,:),B(2,:),'r',A(3,:),B(3,:),'r')

[Alan Stevens]

More generally

for i = 1:numFlr
plot(A(i,:),B(i,:),'r')
end