Error with brackets symsum

f2 = figure;

figure(f2);

ic = linspace(0, 100, K);

[t, n] = ode 45(@(t, n) ODEfunc(n, K);

k_bar = 1/N * symsum(i*n(i),i,0,K);

**I want to solve some ODES eventually with k_bar

I keep getting errors with brackets, im not sure If im tired but i cant spot where its referring to!

Thanks in advance

Answer 1

[Alan Stevens]

Do you mean something more like this?

N = 100; % Total number of particles
one = 1;
alpha = 1;
K = 7; % 7 states

n0 = 4*ones(K,1);
tspan = 0:0.1:5;

[t, n] = ode45(@(t, n) ODEfunc(t, n, K, one, N, alpha), tspan, n0);

plot(t, n),grid
xlabel('time'), ylabel('n')
legend('n1','n2','n3','n4','n5','n6','n7')

function dndt = ODEfunc(~, n, K, one, N, alpha)

S = n(1);
 for i=2:K
     S = i*n(i) + S;
 end
 k_bar = S/N;
 
dndt = zeros(K,1);
 
dndt(1,:) = alpha*n(1)*k_bar - one*n(1);     % Note that this is for state 1.
for i= 2:K-1
dndt(i,:) = alpha*n(i)*(k_bar - i) + one*n(i-1) - one*n(i);  % For state 2 to 6
end
dndt(K,:) = alpha*n(K,1)*(k_bar - K) + one*n(K-1,1);    % For state 7

end

[Alan Stevens]

If N is constant I would expect the sum of dndt over all states to be zero, but it doesn't seem to be.

[Aaron]

Hi, I just realised I forgot to add a -1 with the k_bar, making (k_bar-1) in the first term. It now converges to nice values. thanks for the help on the syntax