Plotting a Piecewise function Dg?

Hello community I look to get the figure of Dg, please verifiy if the definition of Piecewise function Dg is correct and Thank you

clc 
clear all
x=[]; y=[]; z=[];
for n=1:1001
    x1=0.01*(n-1);
 
    x2=4;
    B=[0,x1,4,x2;
        x1,3,x2,x2;
        x1,0,5,x2;
        0,5,x2,x1];
  
    %{
    Pd=eig(B);
    if max(real(Pd))<0
        disp('fail'); 
        disp(n);
    end
    %}
    B11=[B(1,1),B(1,2);B(2,1),B(2,2)];
    B22=[B(3,3),B(3,4);B(4,3),B(4,4)];
    B12=[B(1,3),B(1,4);B(2,3),B(2,4)];
    V1_2=[B11,B12;B12',B22];
A1=det(B11);
B1=det(B22);
C1=det(B12);
D1=det(V1_2);
    Sum=det(B11)+det(B22)+2.*det(B12);
    nup=sqrt(Sum+sqrt(Sum.^2-4.*det(V1_2)))./sqrt(2);
    nun=sqrt(Sum-sqrt(Sum.^2-4.*det(V1_2)))./sqrt(2);
 
    %defin quantum discord
    
fmp=(nup+1)/2*log((nup+1)/2)-(nup-1)/2*log((nup-1)/2);
fmn=(nun+1)/2*log((nun+1)/2)-(nun-1)/2*log((nun-1)/2);
fB1=(sqrt(B1)+1)/2*log((sqrt(B1)+1)/2)-(sqrt(B1)-1)/2*log((sqrt(B1)-1)/2);

Dg1=fB1-fmp-fmn;

%inf epsilon
G1=(2*C1^2+(B1-1)*(D1-A1)+2*abs(C1)*sqrt(C1^2+(-1+B1)*(-A1+D1)))/(B1-1)^2;%val1
G2=(A1*B1-C1^2+D1-sqrt(C1^4+(-A1*B1+D1)^2-2*C1*(A1*B1+D1)))/2*B1;%val2

G3=(D1-A1*B1)^2-(1+B1)*C1^2*(A1+D1);%<=0 condition

DgG1=(sqrt(G1)+1)/2*log((sqrt(G1)+1)/2)-(sqrt(G1)-1)/2*log((sqrt(G1)-1)/2); %val if %G3<=0 condition
DgG2=(sqrt(G2)+1)/2*log((sqrt(G2)+1)/2)-(sqrt(G2)-1)/2*log((sqrt(G2)-1)/2); %else G3>0

if G3 <= 0
       Dg = real(DgG1+Dg1); 
  else     
       Dg = real(DgG2+Dg1);
 end
    
  x(n)=x1; y(n)=Dg; 
    n=n+1;
    
end

plot(x,y)

[John D'Errico]

How can we know if the function is correct, sicne you never tell us what the function should be in terms of mathematics?

Of course it is perfectly correct. It does EXACTLY what the code tells it to do. If it should work differently, then you should have written different code.

[Abdelkader Hd]

I need to define this function which is given in the code as G1 and G2 and the condition as G3. I want to plot this function as a function of other parameters such as temperature and coupling, since the variables A, B, C, and D are indirectly dependent on the mentioned parameters.@John D'Errico

[Abdelkader Hd]