Automated plot using values from an initial graph

I am trying to plot a graph using the the central minima values that are generated from an intial plot.

The attached images and code demonstrate what I am trying to achieve.

clear all;

%PARAMETERS
n1 = 3.43; n2 = 2.97; n0 = 1; n3 = 3.6;
c = 767e-9;    l = 0e-9;    u = 3000e-9;   

              
figure;
CHARTS = tiledlayout('flow');
nexttile;   grid on; grid minor; hold on
xlabel('Wavelength');   ylabel('Angle');   zlabel('Intensity')
zlim ([0 100]);
xlim ([700 800]);

for iRange = 80:-10:0          

np = 20000; s = (u-l)/np;
Wavelength = zeros(1,np);
Intensity = zeros(1,np);
index = 1;

%WAVELENGTH RANGE
for range = l:s:u

incd = iRange*(pi/180);    
a1 = asin((n0*sin(incd))/n1);       
a2 = asin((n1*sin(a1))/n2);     
a21 = asin((n2*sin(a2))/n1);  


%WAVEVECTOR
k = 2*pi/range;          

%THICKNESS
l1 = c/(4*n1); 
l2 = c/(4*n2);

%MATRICES
A = [1 1;n0*cos(a1) -n0*cos(a1)];            
B = [1 1;n1*cos(a21) -n1*cos(a21)];             
C = [1 1;n2*cos(a2) -n2*cos(a2)];
D = [1 1;n3 -n3];


%PROPAGATION
X1 = [exp(1i*k*l1*n1*cos(a21)) 0;0 exp(-1i*k*l1*n1*cos(a21))];
X2 = [exp(1i*k*l2*n2*cos(a2)) 0;0 exp(-1i*k*l2*n2*cos(a2))];


%LAYER
L = X1*(B\C)*X2*(C\B);

M = (A\B)*(L^18)*X2*(L^21)*(B\D);

%REFLECTANCE
E1 = M(2,1)/M(1,1); 
E2 = 100*(abs(E1)^2);

Intensity(index) = E2;
Wavelength(index) = range/1e-9;
index = index+1;
end

[Wv,In] = meshgrid(Wavelength,incd);
plot3(Wv,In,Intensity','linewidth',1)
view(-5,60);           rotate3d('on');

end

Answer 1

[Simon Chan]

Focus on the range of wavelength from 700 to 800 and find the position where abrupt change happens.

%PARAMETERS
n1 = 3.43; n2 = 2.97; n0 = 1; n3 = 3.6;
c = 767e-9;    l = 0e-9;    u = 3000e-9;                
f = figure;
f.Visible = 'off';              % Just make it invisible here
CHARTS = tiledlayout('flow');
nexttile;   grid on; grid minor; hold on
xlabel('Wavelength');   ylabel('Angle');   zlabel('Intensity')
zlim ([0 100]);
xlim ([700 800]);
WvMin = [];                     % Initialize WvMin to store the value of minimum wavelength
iRange = 80:-10:0;              % Set iRange here
for z=1:length(iRange)      
    np = 20000; s = (u-l)/np;
    Wavelength = zeros(1,np);
    Intensity = zeros(1,np);
    index = 1;
    %WAVELENGTH RANGE
    for range = l:s:u
        incd = iRange(z)*(pi/180);    
        a1 = asin((n0*sin(incd))/n1);       
        a2 = asin((n1*sin(a1))/n2);     
        a21 = asin((n2*sin(a2))/n1);  
        %WAVEVECTOR
        k = 2*pi/range;          
        %THICKNESS
        l1 = c/(4*n1); 
        l2 = c/(4*n2);
        %MATRICES
        A = [1 1;n0*cos(a1) -n0*cos(a1)];            
        B = [1 1;n1*cos(a21) -n1*cos(a21)];             
        C = [1 1;n2*cos(a2) -n2*cos(a2)];
        D = [1 1;n3 -n3];
        %PROPAGATION
        X1 = [exp(1i*k*l1*n1*cos(a21)) 0;0 exp(-1i*k*l1*n1*cos(a21))];
        X2 = [exp(1i*k*l2*n2*cos(a2)) 0;0 exp(-1i*k*l2*n2*cos(a2))];
        %LAYER
        L = X1*(B\C)*X2*(C\B);
        M = (A\B)*(L^18)*X2*(L^21)*(B\D);
        %REFLECTANCE
        E1 = M(2,1)/M(1,1); 
        E2 = 100*(abs(E1)^2);
        Intensity(index) = E2;
        Wavelength(index) = range/1e-9;
        index = index+1;
    end
    [Wv,In] = meshgrid(Wavelength,incd);
    plot3(Wv,In,Intensity','linewidth',1)
    view(-5,60);           rotate3d('on');
    minWv = 700;                                    % Focus on wavelength from 700 to 800
    maxWv = 800;
    rangelamda = Wv>700 & Wv<800;                   % Index for wavelength from 700 to 800 
    rangeWv = Wv(rangelamda);                       % Range of wavelength
    rangeIntensity = Intensity(Wv>700 & Wv<800);    % Intensity for this range of wavelength 
    [~,idxMin] = max(gradient(rangeIntensity));     % Find the index of having maximum gradient change
    WvMin = [WvMin rangeWv(idxMin-1)];              % Store the minimum value for each iRange
end
figure(2)
plot(iRange,WvMin,'b-*');
grid on;

[AdomPadom]

Hi,

Thanks for this.

I am getting the following errors when running on the matlab application.

"[~,idxMin] = max(gradient(rangeIntensity)); % Find the index of having maximum gradient change"

How would I solve this? It doesnt occur when running on Matlab online.

[Simon Chan]

Could you restart MATLAB and try once more? And what is the error message?

[AdomPadom]

Apologies - the restart fixed it.

Thank you!