Need help on using ODE45
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John Smith
am 19 Feb. 2015
Bearbeitet: John Smith
am 19 Feb. 2015
I'm trying to solve the following ODE
dx(1)/dt = k1 (1 + k(2)x(3)) − x(1)x(2)^2 − k(3)x(1),
dx(2)/dt = x(1)x(2)^2 − x(2) + k(3)x(1),
dx(3)/dt = x(2) − k(4)x(3),
subject to the initial conditions x(0) = x0 and plot x1, x2 and x3 as a function of t using 10^4 points for 0 ≤ t ≤ T. It should take T and vectors x0 and k0 as inputs.
So far I have the following code:
function crosscatalator(x0,k,T)
sol = ode45(@(t,x) f(t,x,k),[0 T],x0);
t = linspace(0,T,10000); X = deval(sol,t); plot(t,X(1,:),t,X(2,:),t,X(3,:))
legend('x_1','x_2','x_3')
xlabel('t')
function f = f(~,x,k)
f = zeros(3,1);
f(1) = k(1)*(1+k(2)*x(3))-x(1)*x(2)^2-k(3)*x(1);
f(2) = x(1)*x(2)^2-x(2)+k(3)*x(1);
f(3) = x(2)-k(4)*x(3);
When I try with initial conditions x0=[1 1 1], k=[1 2 3 4], T=200. I get an error saying index is out of bounds. I've tried everything I can possibly do to fix this but I keep getting an error. What am I doing wrong?
2 Kommentare
Michael Haderlein
am 19 Feb. 2015
I get the plots, no error occurs. Do you maybe have a variable which is also called "crosscatalator"? If that's not the case, please tell us where exactly the error occurs.
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Mischa Kim
am 19 Feb. 2015
John, your code is good. Is the code above all contained within one file with name crosscatalator.m?
If so, try at the MATLAB command prompt
clear;
x0 = [1 1 1]; k = [1 2 3 4]; T = 200;
crosscatalator(x0,k,T)
and tell us if it is still not working.
8 Kommentare
Mischa Kim
am 19 Feb. 2015
One last (for now) change: re-name the ODE file. Of course, also in the function call, line 2.
function f = myf(~,x,k)
...
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