How to extract variable from a function file while using ode45?
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x = [0.8 -0.2 1 0 0 0.8 -0.2]';
tspan = [0 20];
[t,x]= ode45(@(t,x) fun(t,x),tspan,x);
function [dot] = fun(t,x)
k1 = 3;
k2 = 3;
k3 = 3;
x1 = x(1);
x2 = x(2);
x3 = x(3);
z2 = x(4);
z3 = x(5);
S1 = x(6);
S2 = x(7);
yr = sin(t);
s1 = x1 - yr;
s2 = x2 - z2;
s3 = x3 - z3;
tau2 = exp(-t) + 0.05;
tau3 = exp(-t) + 0.05;
alpha2 = -k1*s1 - (x1^2 + x2^3 +x3 -x2) + cos(t);
z2dot = (alpha2 - z2)/tau2;
alpha3 = -k2*s2 - (x1^2*x2 + x3^5 - x3) + z2dot;
z3dot = (alpha3 - z3)/tau3;
u = -k3*s3 - x1*x2*x3^2 + z3dot;
x1dot = x1^2 + x2^3 + x3;
x2dot = x1^2*x2 + x3^5;
x3dot = u + x1*x2*x3^2;
S1dot = x1dot - cos(t);
S2dot = x2dot - z2dot;
dot = [x1dot x2dot x3dot z2dot z3dot S1dot S2dot]';
For example, I want to extract variable u from this code, is it possible to do so?
1 commentaire
Jan
le 20 Mar 2021
Please use the tools for formatting code in the forum. I've done this for you this time.
Réponse acceptée
Jan
le 20 Mar 2021
Modifié(e) : Jan
le 20 Mar 2021
This question is asked several times per day. I ask MathWorks to include an explanation in the documentation.
Yes, of course it is possible. Simply modify the function to be integrated such, that it accepts vectors as input and use the output of ODE45 as input. There is a tricky need to transpose the inputs:
[t, x] = ode45(@fun, tspan, x); % @fun is faster than @(t,x) fun(t,x)
[~, u] = fun(t.', x.');
function [dot, u] = fun(t, x)
k1 = 3;
k2 = 3;
k3 = 3;
x1 = x(1, :);
x2 = x(2, :);
x3 = x(3, :);
... etc.
% Use elementwise operators: * ==> .* , ^ ==> .^ , / ==> ./
end
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prabhjeet singh
le 20 Mar 2021
7 commentaires
Jan
le 22 Mar 2021
"if I edit code as per your suggestion" - this still does not allow to understand, what you are doing to obtain different values for yr. You just show one of the methods, but what is the other?
[~ , u, yr] = fun(t.', x.');
figure;
plot(t, yr);
hold on
plot(t, sin(t), 'ro');
function [dot,u,yr] = fun(t,x)
...
yr = sin(t);
...
end
Except for transposition of the vector both outputs are equal.
You questions about Matlab are welcome in this forum. You do not "bother", but try to solve a problem. This is the purpose of this forum and if I do not find the time to assist you, somebody else will do this.
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