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can anyone help me with "ode45" ?

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ADNAN KIRAL
ADNAN KIRAL on 25 Nov 2018
Closed: MATLAB Answer Bot on 20 Aug 2021
Hi
i do have a function like;
function [xdot,NOD]=random_func(t,x)
.
.
.
end
and a "ode45" like
[t,x]=ode45(@random_func,tspan,x0,cn3);
I would like to take "NOD" out given in my function;
How can I get it in a ".mat" ? is that possible? Or I need to use the Runge Kutta method manually?
Please a bit urgent, thanks in advance. If you want a clear understanding, I can upload a draft code.
  2 Comments
ADNAN KIRAL
ADNAN KIRAL on 27 Nov 2018
i see, will consider that. thanks for your reply.

Answers (1)

Star Strider
Star Strider on 25 Nov 2018
Probably the easiest way would be to integrate your function first, the using the solved values for ‘t’ and ‘x’, run it again, recover the ‘NOD’ output, and save it.
Example —
function [xdot,NOD]=random_func(t,x)
xdot(1,:) = t-x(1); % Create Equation
xdot(2,:) = t+x(2); % Create Equation
NOD = rand; % Create ‘NOD’
end
tspan = [0 1];
x0 = [1;1];
[T,X] = ode45(@random_func, tspan, x0);
figure
plot(T, X)
grid
NODv = zeros(numel(T),1); % Preallocate
for k1 = 1:numel(T)
[~,NOD(k1,:)] = random_func(T(k1),X(k1,:)); % Calculate ‘NOD’, Save As Vector
end
fprintf(1, '%.4f,%.4f\n', [T NOD]') % Save Data
I simply printed out the ‘NOD’ vector here (alternatively saving it as a ‘.csv’ file with the same statement although with an appropriate file identification number created by fopen), since I did not want to create the file and then have to delete it. Use the appropriate save syntax to create your ‘.mat’ file.
This illustrates the idea. You will likely need to experiment with it and tweak it to make it work with your functions.

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