Eigenvalue output in different order to inputs

Hi, This code is meant to plot the mode shapes of buildings. Is it possible to have the eigenvalues outputted in ascending order and have the eigen vectors follow this order too?

For example, if eigenvalues were: 2,3,1 ; I would like to be in the order 1,2,3. But also have the eigenvectors arranged in a manner that I know what eigenvector corresponds to each eigenvalue.

Here is my code below:

clear all

numFlr=input('Number of floors: ');
MVal=zeros(numFlr,1);
EVal=zeros(numFlr,1);
IVal=zeros(numFlr,1);
LVal=zeros(numFlr,1);
KVal=zeros(numFlr,1);
K=zeros(numFlr,1);

for i=1:numFlr
    MVal(i)=input('Mass:');
    EVal(i)=input('Elastic Modulus:');
    IVal(i)=input('Second Moment of Area:');
    LVal(i)=input('Length:');
end
for i=1:numFlr
    KVal(i)=(24*EVal(i)*IVal(i))/(LVal(i)^3);
end

M=diag(MVal);

%stiffness matrix
for i=1:numFlr
    for j=1:numFlr
        try
            if i==j
                K(i,j)=(KVal(i)+KVal(i+1));
            elseif j==i+1
                K(i,j)=-KVal(j);
            elseif i==j+1
                K(i,j)=-KVal(i);
            end
        end
    end
end

K(end,end)=KVal(end,:);
K=K

%eigenvalues and eigenvectors
Omega2=eig(K,M);
Omega=sqrt(Omega2);
A=inv(M)*K;
[Vec,Val,Vec2]=eig(A);
Omega2_EigVal=diag(Val)
EigVec=Vec
OmegaSpecial=sqrt(Omega2_EigVal)

%plotting arrays
Choose=input('Mode: ');
y1=zeros(numFlr,1);
y2=zeros(numFlr,1);
x1=zeros(numFlr,1);
x2=EigVec(:,Choose);

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

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

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

Examples of input values would be:

Number of floors: 5

Mass:2

Elastic Modulus:1

Second Moment of Area:1

Length:1

Mass:1

Elastic Modulus:1

Second Moment of Area:1

Length:1

Mass:2

Elastic Modulus:1

Second Moment of Area:1

Length:1

Mass:2

Elastic Modulus:1

Second Moment of Area:1

Length:1

Mass:1

Elastic Modulus:1

Second Moment of Area:1

Length:1

I was thinking of using sort but I am unsure how I could implement this when using eig().

Answer 1

[Matt J]

Omega2=sort(eig(K,M));

...

[Vec,Val,Vec2]=eig(A);

[~,ind]=sort(diag(Val))
Vec=Vec(:,ind);
Val=Val(:,ind);
Vec2=Vec2(:,ind);

[Joshua Tsui]

Thankyou. I will test this out now.

[Joshua Tsui]

Hi Matt. I have tried out your solution. For some reason, I am no longer getting a diagonal matrix for Val when applying your solution.

[Joshua Tsui]

Actually, I believe this may have solved the problem due to a previous line of code giving me access to values of Val.