How to extract variable from a function file while using ode45?
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prabhjeet singh
el 20 de Mzo. de 2021
Comentada: Jan
el 22 de Mzo. de 2021
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 comentario
Jan
el 20 de Mzo. de 2021
Please use the tools for formatting code in the forum. I've done this for you this time.
Respuesta aceptada
Jan
el 20 de Mzo. de 2021
Editada: Jan
el 20 de Mzo. de 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
el 20 de Mzo. de 2021
7 comentarios
Jan
el 22 de Mzo. de 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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