I'm having this error in code "Index in position 2 exceeds array bounds. Index must not exceed 20." can a nyone please explain how can I get rid of this?

clc
clear
ti = 0;
tf = 7E-5;
tp = 1E-9;
tspan= [0:1E-7:7E-5]./tp;
KC = 1;
h = 1E-2;
N = 20;
y0 = zeros(3*N*N,1);

for j = 1:N*N
    
    y0(3*j,1) = (-3.14).*rand(1,1) + (3.14).*rand(1,1);
    
end
y0;

for j = 1:3*N*N
    if y0(j,1) == 0
        y0(j,1) = (h)*rand(1,1);
    else 
        y0(j,1) = y0(j,1);
    end
end
y0

y0 = 1200×1

0.0080 0.0009 1.0877 0.0014 0.0090 2.0797 0.0039 0.0064 -0.4429 0.0011

L = 1

L = 1

C = zeros(N,N);
for i = 1:N
    for j = 1:N
        if i ~= j
            C(i,j) = 1;
        end
    end
end

yita_mn = C.*2E-3

yita_mn = 20×20

0 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020 0.0020

tp = 1E-9;
o = sort(10e2*rand(1,N*N),'ascend');
[T,Y]= ode45(@(t,y) rate_eq(t,y,yita_mn,o),tspan,y0);

Index in position 2 exceeds array bounds. Index must not exceed 20.

Error in solution>rate_eq (line 68)
dAdt(i) = dAdt(i) + yita_mn(i,j)*(At(j))*cos(Ot(j)-Ot(i)) + yita_mn(j,i)*(At(j))*cos(Ot(j)-Ot(i));

Error in solution>@(t,y)rate_eq(t,y,yita_mn,o) (line 41)
[T,Y]= ode45(@(t,y) rate_eq(t,y,yita_mn,o),tspan,y0);

Error in odearguments (line 92)
f0 = ode(t0,y0,args{:}); % ODE15I sets args{1} to yp0.

Error in ode45 (line 107)
odearguments(odeIsFuncHandle,odeTreatAsMFile, solver_name, ode, tspan, y0, options, varargin);

figure(3)
plot(T,(Y(:,3)),'linewidth',2);


function dy = rate_eq(t,y,yita_mn,o)
N = 20;
dy = zeros(3*N*N,1);
dGdt = zeros(N*N,1);
dAdt = zeros(N*N,1);
dOdt = zeros(N*N,1);
P = 0.4;
a = 0;
T = 800;
tp = 1E-9;
Gt = y(1:3:3*N*N-2);
At = y(2:3:3*N*N-1);
Ot = y(3:3:3*N*N-0);
k = 1E-3;
for i = 1:N*N
    dGdt(i) = (P - (Gt(i)) - (1 + 2.*Gt(i)).*((At(i)))^2)./T ;
    dAdt(i) = Gt(i)*(At(i));
    dOdt(i) = (-a).*(Gt(i)) + o(1,i).*tp;  
    for j = 1:N*N
        dAdt(i) = dAdt(i) + yita_mn(i,j)*(At(j))*cos(Ot(j)-Ot(i)) + yita_mn(j,i)*(At(j))*cos(Ot(j)-Ot(i));
        dOdt(i) = dOdt(i) + yita_mn(i,j)*((At(j)/At(i)))*sin(Ot(j)-Ot(i));
    end
end
dy(1:3:3*N*N-2) = dGdt;
dy(2:3:3*N*N-1) = dAdt;
dy(3:3:3*N*N-0) = dOdt;
end

=========================================================================================

Index in position 2 exceeds array bounds. Index must not exceed 20.

Error in twodlaserarray>rate_eq (line 116)

dAdt(i) = dAdt(i) + yita_mn(i,j)*(At(j))*cos(Ot(j)-Ot(i)) + yita_mn(j,i)*(At(j))*cos(Ot(j)-Ot(i));

Error in twodlaserarray (line 41)

[T,Y]= ode45(@(t,y) rate_eq(t,y,yita_mn,o),tspan,y0);

Error in odearguments (line 92)

f0 = ode(t0,y0,args{:}); % ODE15I sets args{1} to yp0.

Error in ode45 (line 107)

odearguments(odeIsFuncHandle,odeTreatAsMFile, solver_name, ode, tspan, y0, options, varargin);

=========================================================================================

[Sathvik]

The 'yita_mn' variable is a 20*20 matrix, while the indices i and j are between 1 and 400 in the for loop within the function. Modify the loop accordingly and it should work.

Answer 1

[Shivani]

Hi Sahil,

The reason why you are getting an index out of bounds error is because the limits of the for loop exceed the dimensions of the array that you are trying to index into within the loop body. I understand that you’re using two variables i and j to index into the matrix yita_mn within the loop body. However, the matrix is of dimension 20*20 i.e. you have 20 rows and 20 columns in your matrix. Therefore, your max limit for i and j should be 20 and not 20*20. 0

You will have to modify your loop conditions to something like this to successfully loop through the matrix

for i = 1:N 
    dGdt(i) = (P - (Gt(i)) - (1 + 2.*Gt(i)).*((At(i)))^2)./T ; 
    dAdt(i) = Gt(i)*(At(i)); 
    dOdt(i) = (-a).*(Gt(i)) + o(1,i).*tp;   
    for j = 1:N 
        dAdt(i) = dAdt(i) + yita_mn(i,j)*(At(j))*cos(Ot(j)-Ot(i)) + yita_mn(j,i)*(At(j))*cos(Ot(j)-Ot(i)); 
        dOdt(i) = dOdt(i) + yita_mn(i,j)*((At(j)/At(i)))*sin(Ot(j)-Ot(i)); 
    end 
end 

You can look at the official documentation for more insights regarding indexing: Matrix Indexing in MATLAB - MATLAB & Simulink (mathworks.com)

Hope this helps!