CODEWITHSUNDEEP
matlabplotmatlab-figure
Jack
Jack

Reputation: 1

Empty plot in MATLAB

I am trying to plot Reflection coefficient by using this formula:

enter image description here

Code:

E1=1;
E2=2.32*E1; 

for tetai=1:90      
    numerator=cos(tetai)-(sqrt(E2/E1).*sqrt(1-(E1/E2).*sin(tetai)^2));
    denominator=cos(tetai)+(sqrt(E2/E1).*sqrt(1-(E1/E2).*sin(tetai)^2));
    eta=numerator/denominator;
    plot(tetai,eta,'r');
    hold on
end     

title('Plots')
xlabel('\Theta')
ylabel('\Gamma')

After repeating E2 values with 2.56, 4, 9, 16, 25, and 81 I should obtain the following result (At first step I just wanted to obtain a single value with E2=2.32):

enter image description here

But unfortunately, there is no graphics on the plot result screen. So, what is the mistake?

Note: I use MATLAB R2015a

Upvotes: 0

Views: 1392

Answers (2)

Sardar Usama
Sardar Usama

Reputation: 19689

Mistakes:

  1. You're using sin and cos and inputting angle in degrees. Either convert the angle or even better use the functions dedicated for this purpose. i.e sind and cosd respectively.

  2. You don't see anything in output because you're plotting point by point. For that, some marker should've been specified. But anyway, what you want to plot is not this. You want to plot a line instead.

  3. Another problem in using plot is that you are not plotting what you think you should be plotting. The image that you showed in the question is a plot between |Γᵇ⊥| and θᵢ , not Γᵇ⊥ and θᵢ

Fixed code:

E1=1;
E2i=[2.32, 2.56, 4, 9, 16, 25, 81];

gamma = zeros(1,91);    %Pre-allocation
for k=1:7
    E2 = E2i(k);

    for theta_i=0:90
        numerator=cosd(theta_i)- sqrt((E2/E1)*(1-(E1/E2)*sind(theta_i)^2));
        denominator=cosd(theta_i)+ sqrt((E2/E1)*(1-(E1/E2)*sind(theta_i)^2));
        gamma(theta_i+1)=numerator/denominator;    
    end

    plot(0:90,abs(gamma));
    hold on;
    text(45,abs(gamma(45)),['\epsilon_2/\epsilon_1  = ',num2str(E2/E1)]);
end

title('Plots');  xlabel('\theta_i (degrees)');  ylabel('|\Gamma^b_\perp|');

Output:

Output

Upvotes: 10

lnyng
lnyng

Reputation: 965

You can try create a nan vector outside the loop, fill the vector in the iterations, and plot outside the loop.

E1=1;
E2=2.32*E1; 
Data=nan(90);

for tetai=1:90      
    numerator=cos(tetai)-(sqrt(E2/E1).*sqrt(1-(E1/E2).*sin(tetai)^2));
    denominator=cos(tetai)+(sqrt(E2/E1).*sqrt(1-(E1/E2).*sin(tetai)^2));
    eta=numerator/denominator;
    Data(tetai)=eta;
end     

plot(Data, 'r');
title('Plots')
xlabel('\Theta')
ylabel('\Gamma')

Edited on phone, not tested.

Upvotes: 1

Related Questions