I want to check time series of the ordinary differential equation of 10 dimension .summed over all patches

clc;
clear all;
n = 20;
x=accumarray([2 3 n-1 n]',1);
B = toeplitz(x,x);

numEdgesToRewire = 2;  


matrixSize=20;

edgesToRewire = randperm(matrixSize, numEdgesToRewire);


for i = 1:numEdgesToRewire
    node1 = edgesToRewire(i);
    node2 = randi([1, matrixSize]);
    
    
    while node2 == node1 || B(node1, node2) == 1
        node2 = randi([1, matrixSize]);
    end
    
    B(node1, node2) = 1;
    B(node2, node1) = 1;
end
disp(B)
theta = 0.3;
dh = 2^-9;
dp = 2^-7;
phi = 3;
ita = 1;

y=[x(1);x(2);x(3);x(4);x(5);x(6);x(7);x(8);x(9);x(10);x(11);x(12);x(13);x(14);x(15);x(16);x(18);x(19);x(20)]

x0 = rand(1,20);

i = 1;
f = [];

function xprime = kau(t, x, B)
nn = length(x); 

while i <= nn  
    f = [f; x(i)*(1 - theta*x(i)) - x(i+1) - (x(i)*x(i+1)) / (1 + x(i+1)); ...
        (phi*x(i)*x(i+1)) / (1 + x(i+1)) - ita*x(i+1)];
    i = i + 1;  
end

xprime = f+B*y;  
end

[t,x]=ode45(@(kau(t, x, B),tspan, x0);

H=x(1)+x(3)+x(5)+x(7)+x(9)+x(11)+x(13)+x(15)+x(17)+x(19);
P=x(2)+x(4)+x(6)+x(8)+x(10)+x(12)+x(14)+x(16)+x(18)+x(20);

plot(t, H, 'b');

hold on
plot(t, P, 'r');

[Rik]

Let's clean up this code a bit:

clc;
%clear all; % <--- This is a bad habit. Do you reboot your computer every
%time you run this script? Of course you don't. Then don't use this. At
%most you'll need clearvars.
n = 20;
x=accumarray([2 3 n-1 n]',1);
% This is a very strange way to do this (especially without a comment)
% This is a lot clearer:
x=zeros(n,1);x([2 3 end-1 end])=1;

B = toeplitz(x,x);

numEdgesToRewire = 2;  
matrixSize=20; % Should this perhaps be matrixSize=size(B,1);? Or n?
edgesToRewire = randperm(matrixSize, numEdgesToRewire);

for n = 1:numEdgesToRewire % use n as loop index
    node1 = edgesToRewire(n);
    % node2 = randi([1, matrixSize]);
    node2 = node1; % this will already enter the loop
    while node2 == node1 || B(node1, node2) == 1
        node2 = randi([1, matrixSize]);
    end
    
    B(node1, node2) = 1;
    B(node2, node1) = 1;
end
disp(B)
theta = 0.3;
dh = 2^-9;
dp = 2^-7;
phi = 3;
ita = 1;

% y=[x(1);x(2);x(3);x(4);x(5);x(6);x(7);x(8);x(9);x(10);x(11);x(12);x(13);x(14);x(15);x(16);x(18);x(19);x(20)]
% This is not a matlab way to do it. Use indexing instead:
y = x(setdiff(1:end,17)); % did you indeed want to remove element 17?

x0 = rand(1,20);

% i = 1; % you aren't using i in your code
% f = []; % you aren't using f in your code

% [t,x]=ode45(@(kau(t, x, B),tspan, x0);
% After resolving the syntax errors, you will need to define two variables:
tspan = 
x0 =
[t,x]=ode45(@kau,tspan, x0);

%H=x(1)+x(3)+x(5)+x(7)+x(9)+x(11)+x(13)+x(15)+x(17)+x(19);
%P=x(2)+x(4)+x(6)+x(8)+x(10)+x(12)+x(14)+x(16)+x(18)+x(20);
% again; use indexing
H = x(1:2:end);
P = x(2:2:end)

plot(t, H, 'b');
hold on
plot(t, P, 'r');
hold off

function xprime = kau(t, x, B)
nn = length(x); 

while i <= nn  
    f = [f; x(i)*(1 - theta*x(i)) - x(i+1) - (x(i)*x(i+1)) / (1 + x(i+1)); ...
        (phi*x(i)*x(i+1)) / (1 + x(i+1)) - ita*x(i+1)];
    i = i + 1;  
end

xprime = f+B*y;  
end

[Rik]

Your code does not have any comments. It is therefor completely useles to anyone but you. And once you forget why you did exactly what you did, you will no longer be able to use it either. You should comment your code, explain what it is doing and why. That will help others find out what needs to change, and will help you remember what you did.

[William Rose]

That was a very thoughtful and constructive analysis from @Rik.

To which I would also add, please post the simplest version of your code that illustrates the problem you want to solve. I realize it is more work for you to make a slimmed-down version, but it is a courtesy to those who might help you, and is more likely to get you the answers you need.

Please explain what you mean by "I want to check time series of the ordinary differential equation of 10 dimension .summed over all patches".