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Error with brackets symsum

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Aaron on 22 Dec 2022
Edited: Aaron on 23 Dec 2022
f2 = figure;
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

Answers (1)

Alan Stevens
Alan Stevens on 22 Dec 2022
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')
function dndt = ODEfunc(~, n, K, one, N, alpha)
S = n(1);
for i=2:K
S = i*n(i) + S;
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
dndt(K,:) = alpha*n(K,1)*(k_bar - K) + one*n(K-1,1); % For state 7
Alan Stevens
Alan Stevens on 22 Dec 2022
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 on 22 Dec 2022
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

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