Why my plot is blank?

clc
clear all
close all
w0=73000;
S=950;
AR=5.92;
C_D0=0.015;
K=0.08;

rho=8.9068*10^-4;
for V=300:100:1300
    CL=(2*w0)/(rho*V^2*S);
    CD=C_D0+K*CL^2;
    Tr=0.5*rho*V^2*S*CD;
    disp([' At free stream velcoity  ', num2str(V), ' m/s, CL is  ', num2str(CL), ' , CD is ', num2str(CD) ' , Tr is ', num2str(Tr)]);
end
plot(V,Tr)

Answer 1

[Image Analyst]

You didn't index V or Tr. Try this:

clc
clear all
close all
w0=73000;
S=950;
AR=5.92;
C_D0=0.015;
K=0.08;

rho=8.9068*10^-4;
allV=300:100:1300
Tr = zeros(1, length(allV));
for k = 1 : length(allV)
    V = allV(k);
    CL=(2*w0)/(rho*V^2*S);
    CD=C_D0+K*CL^2;
    Tr(k)=0.5*rho*V^2*S*CD;
    fprintf(' At free stream velocity  %d m/s, CL is  %f, CD is %f, Tr is %f\n', ...
        V, CL, CD, Tr(k));
end
plot(allV, Tr, 'b.-', 'LineWidth', 2, 'MarkerSize', 30)
grid on;
xlabel('V', 'FontSize', 15);
ylabel('Tr', 'FontSize', 15);

Answer 2

[Cris LaPierre]

The most likely reason is that V and Tr are a single number. By default, MATLAB does not plot using markers, so if there is only a single point, you won't see it.

See this answer for how to create a vector using a for loop.