Declaring an anonymous function for solving an odes system
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Hi there,
I am trying to integrate a system of ODES, I am being partially successful defining the function in another file, but when trying to do that using an anonymus function, it is not working, I am not sure what is wrong.
So, the working version is:
in F.m file:
function x = F(t,theta)
N = 10; lambda = 1; k = 4;
omega = lambda*tan(pi*(rand(1,N)-0.5));
x = omega' + k/N*sum(sin(repmat(theta,[1 N])' - repmat(theta,[1 N])),2);
and then:
N = 10;
[t,x] = ode45(@F,[0,10],ones(N,1));
And the one Im trying to make work is:
N = 10; lambda = 1; k = 4;
omega = lambda*tan(pi*(rand(1,N)-0.5));
FK = @(t,theta) omega' + k/N*sum(sin(repmat(theta,[1 N])' - repmat(theta,[1 N])),2) ;
[t,x] = ode45(FK,[0,10],ones(N,1));
Thanks in advance
2 Comments
Adam
on 29 Sep 2015
What do you mean by 'not working'? Is there an error message or are you just getting incorrect results?
Accepted Answer
gringer45
on 29 Sep 2015
1 Comment
Walter Roberson
on 29 Sep 2015
No, the other way around. When you use rand() or randn() in your ODE function, you make the function discontinuous and non-repeatable. This would drive the integrator to smaller and smaller step sizes unless you are using a fixed-step solver. If you must have randomness, you should define the random contributions ahead of time, possibly with some method of interpolating at interior times.
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