plot lines not showing up

clc
clear
format long
R=287;
r=1.4;
Mach=[2:0.5:6];
for i=1:9
    M=Mach(1,i);
   for density=1.225
       To=300;
       p=101325;
       ao=sqrt(r*R*To);
       V=ao*M;
       m=M^2;
       P=p*(((2*r*m)-(r-1))/(r+1));
       D=density*(((r+1)*m)/(((r-1)*m)+2));
       Q=(D*((V^2)/2));
       Po=P+Q;
       plot(Po,P,'r*')
       hold on
   end
   for density=1.203
       To=284.9;
       p=99507.54;
         ao=sqrt(r*R*To);
         V=ao*M;
         m=M^2;
         D=density*(((r+1)*m)/(((r-1)*m)+2));
         Q=D*((V^2)/2);
         P=p*(((2*r*m)-(r-1))/(r+1));
         Po=P+Q;
         plot(Po,P,'ko')
       hold on
   end
end
hold off
xlabel('Po')
ylabel('P')
legend('Wind Tunnel','FL500','Location','northwest')

[Ankit Sahay]

Please follow the community guidelines while asking questions. In short, explain what are you asking, why and what steps have you taken to solve your problem. Write your question in a way that a layman who has no idea of what you are trying to do can understand.

Answer 1

[KSSV]

You can save the generated values into a vector/ matrix and plot at the end. Check the below code:

clc
clear
format long
R=287;
r=1.4;
Mach=[2:0.5:6];
x = zeros(9,2) ; 
y = zeros(9,2) ; 
for i=1:9
    M=Mach(1,i);
   for density=1.225
       To=300;
       p=101325;
       ao=sqrt(r*R*To);
       V=ao*M;
       m=M^2;
       P=p*(((2*r*m)-(r-1))/(r+1));
       D=density*(((r+1)*m)/(((r-1)*m)+2));
       Q=(D*((V^2)/2));
       Po=P+Q;
       plot(Po,P,'r*')
       hold on
       x(i,1) = Po ;
       y(i,1) = P ; 
   end
   for density=1.203
       To=284.9;
       p=99507.54;
         ao=sqrt(r*R*To);
         V=ao*M;
         m=M^2;
         D=density*(((r+1)*m)/(((r-1)*m)+2));
         Q=D*((V^2)/2);
         P=p*(((2*r*m)-(r-1))/(r+1));
         Po=P+Q;
         plot(Po,P,'ko')
       hold on
       x(i,2) = Po ;
       y(i,2) = P ; 
   end
end
hold off
xlabel('Po')
ylabel('P')

figure
plot(x,y)

Answer 2

[Alan Stevens]

You were overwriting P all the time, instead of storing all the values:

R=287;
r=1.4;
Mach=[2:0.5:6];
for i=1:9
    M=Mach(1,i);
   for density=1.225
       To=300;
       p=101325;
       ao=sqrt(r*R*To);
       V=ao*M;
       m=M^2;
       P(i)=p*(((2*r*m)-(r-1))/(r+1)); %%%%%%%%%%%%%%%%%%%%%%%%
       D=density*(((r+1)*m)/(((r-1)*m)+2));
       Q=(D*((V^2)/2));
       Po(i)=P(i)+Q;   %%%%%%%%%%%%%%%%%%%%%%%%%%%%%
       plot(Po,P,'r*')
       hold on
   end
   for density=1.203
       To=284.9;
       p=99507.54;
         ao=sqrt(r*R*To);
         V=ao*M;
         m=M^2;
         D=density*(((r+1)*m)/(((r-1)*m)+2));
         Q=D*((V^2)/2);
         P2(i)=p*(((2*r*m)-(r-1))/(r+1)); %%%%%%%%%%%%%%%%%%%%%%%%%%%%
         Po2(i)=P2(i)+Q;                 %%%%%%%%%%%%%%%%%%%%%%%
         plot(Po2,P2,'ko')
       hold on
   end
end
hold off
xlabel('Po')
ylabel('P')
legend('Wind Tunnel','FL500','Location','northwest')

[KSSV]

You have not intialized P1,P2,Po1,Po2.....

Every time they are being plotted in loop.