Problem in Eigen values plot

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AVM
AVM on 25 Jun 2020
Commented: AVM on 28 Jun 2020
I would like to plot the First five minimum eigenvalues in assending order w.r.t. ''g '' of the following Matrix using for loop. But am really confuse to sort the minimum eigevlaues. Can anybody help me to solve that?
clc;
syms g
omega=1.0;
D = 1.0;
n=15;
I1=eye(n);
I2=eye(2);
matdimension= n-1;
tempvector = 0:1:matdimension;
tempvector = sqrt(tempvector);
tempmatrix = diag(tempvector);
anni= circshift(tempmatrix,-1);
crea = anni';
sc=(crea)^2;
sanni=(anni)^2;
num=crea*anni;
c=crea+anni;
d=sc+sanni;
sigx=[0,1;1,0];
sigy=[0,-1i;1i,0];
sigz=[1,0; 0,-1];
sigp=(1/2)*(sigx+1i.*sigy);
sigm=(1/2)*(sigx -1i.*sigy);
g=0:0.01:2.0;
for i = 1:length(g)
A= omega.*kron(I2,num) + (D./2).* kron(sigz,I1) + g(i).*kron(sigx,c);
[~,v]=eig(A);
end
%plot(g,p1,'r',g,p2,'r',g,p3,'r',g,p4,'r',g,p5,'r')
%ax = gca;
%set(gca,'XMinorTick','on','YMinorTick','on')

Accepted Answer

Takumi
Takumi on 26 Jun 2020
Using sort function, you can sort the elements of matrix in ascending order.
clc;
close all
clear
syms g
omega=1.0;
D = 1.0;
n=15;
I1=eye(n);
I2=eye(2);
matdimension= n-1;
tempvector = 0:1:matdimension;
tempvector = sqrt(tempvector);
tempmatrix = diag(tempvector);
anni= circshift(tempmatrix,-1);
crea = anni';
sc=(crea)^2;
sanni=(anni)^2;
num=crea*anni;
c=crea+anni;
d=sc+sanni;
sigx=[0,1;1,0];
sigy=[0,-1i;1i,0];
sigz=[1,0; 0,-1];
sigp=(1/2)*(sigx+1i.*sigy);
sigm=(1/2)*(sigx -1i.*sigy);
g=0:0.01:2.0;
for i = 1:length(g)
A= omega.*kron(I2,num) + (D./2).* kron(sigz,I1) + g(i).*kron(sigx,c);
[~,v]=eig(A);
V=diag(v);
Vsort = sort(V);
Vsort(1) % minimum eigenvalue
Vsort(1:5) % First five minimum eigenvalues
end

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