Want to use nested For loop

Hello,

I wish to change value of k in my code after running the code for all j values and then, I wish to plot for the curves for different k values in a single window. But I am confused in putting the index values.

n0 = 1;
n1 = 2;
n2 = 1;
n3 = 2;
d1 = 0.1;
d2 = 0.2;
lam = 3:0.01:7;
th = 0;
phi1 =(d1./lam).*sqrt((n1));
phi2 = (d2./lam).*sqrt((n2));
z = zeros(size(lam));
for k = 1:1:6
    for j = 1:numel(lam)
        D0 = [2 2;  n0 -n0];
        D1 = [2 2;n1 -n1];
        D2 = [2 2; n2 -n2];
        D3 = [2 2;n3 -n3];
        P1 = [exp(-1i.*phi1(j)) 1; 1 exp(1i.*phi1(j))];
        P2 = [exp(-1i*phi2(j)) 1; 1 exp(1i*phi2(j))];
        M = D0*([D1*P1*D2*P2]^(k))*D3;
        z(j) = M(2,1)./M(1,1);
    end
end
plot(lam,z);

Answer 1

[chicken vector]

You need to add a second dimension to your z array:

n0 = 1;
n1 = 2;
n2 = 1;
n3 = 2;
d1 = 0.1;
d2 = 0.2;
lam = 3:0.01:7;
th = 0;
phi1 =(d1./lam).*sqrt((n1));
phi2 = (d2./lam).*sqrt((n2));
z = zeros(length(lam),6); % each column corresponds to a different value of k
for k = 1:1:6
    for j = 1:numel(lam)
        D0 = [2 2;  n0 -n0];
        D1 = [2 2;n1 -n1];
        D2 = [2 2; n2 -n2];
        D3 = [2 2;n3 -n3];
        P1 = [exp(-1i.*phi1(j)) 1; 1 exp(1i.*phi1(j))];
        P2 = [exp(-1i*phi2(j)) 1; 1 exp(1i*phi2(j))];
        M = D0*([D1*P1*D2*P2]^(k))*D3;
        z(j,k) = M(2,1)./M(1,1); % add column variable 'k' to z
    end
end
plot(lam,z);

Now z is a 401x6 array where each column corresponds to a different value of k.

For example, you can access your curve at k=3 as:

k = 3;
curve3 = z(:,k);

Notice that this code will generate 6 identical lines therefore you will see only one, but that depends on how you define z.

When you do M(2,1)./M(1,1) the value of k cannot influence the result because it applies identically to both numerator (M(2,1)) and denominator (M(1,1)).

[Ashi Khajotia]

Thanks a lot for your help :D

Answer 2

[Mathieu NOE]

hello

here you are

also you are plotting a complex valued array, so I assume you wanted to take the bas of it first

abs(z) seems to be always equal to 0.5 whatever k and lam (reduced the spacing for faster rendering)

n0 = 1;
n1 = 2;
n2 = 1;
n3 = 2;
d1 = 0.1;
d2 = 0.2;
lam = 3:0.1:7;
th = 0;
phi1 =(d1./lam).*sqrt((n1));
phi2 = (d2./lam).*sqrt((n2));


for k = 1:1:6
    z = zeros(size(lam));
     for j = 1:numel(lam)
            D0 = [2 2;  n0 -n0];
            D1 = [2 2;n1 -n1];
            D2 = [2 2; n2 -n2];
            D3 = [2 2;n3 -n3];
            P1 = [exp(-1i.*phi1(j)) 1; 1 exp(1i.*phi1(j))];
            P2 = [exp(-1i*phi2(j)) 1; 1 exp(1i*phi2(j))];
            M = D0*([D1*P1*D2*P2]^(k))*D3;
            z(j) = M(2,1)./M(1,1);
     end
 
 leg_str{k} = ['k = ' num2str(k)];
 plot(lam,abs(z));hold on
 
end
legend(leg_str);

[Ashi Khajotia]

Thank you for your help!! :D

Answer 3

[Walter Roberson]

n0 = 1;
n1 = 2;
n2 = 1;
n3 = 2;
d1 = 0.1;
d2 = 0.2;
lam = 3:0.01:7;
th = 0;
phi1 =(d1./lam).*sqrt((n1));
phi2 = (d2./lam).*sqrt((n2));
z = zeros(size(lam));

ax1 = subplot(2,1,1);
ax2 = subplot(2,1,2);

for k = 1:1:6
    for j = 1:numel(lam)
        D0 = [2 2;  n0 -n0];
        D1 = [2 2;n1 -n1];
        D2 = [2 2; n2 -n2];
        D3 = [2 2;n3 -n3];
        P1 = [exp(-1i.*phi1(j)) 1; 1 exp(1i.*phi1(j))];
        P2 = [exp(-1i*phi2(j)) 1; 1 exp(1i*phi2(j))];
        M = D0*([D1*P1*D2*P2]^(k))*D3;
        z(j) = M(2,1)./M(1,1);
    end
    plot(ax1, lam, real(z), 'DisplayName', "real k = " + k);
    hold(ax1, 'on');
    plot(ax2, lam, imag(z), 'DisplayName', "imag k = " + k);
    hold(ax2, 'on');
end
hold(ax1, 'off');
legend(ax1, 'show');
hold(ax2, 'off');
legend(ax2, 'show')

The reason you only see one line on each graph is that all of the values are the same to within the tolerance of the graph.