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I want to pass additional parameters to the ode45 function in MATLAB. There are many questions already on this, but I also have a 'flag' argument in my function.

function [xdot,isterminal,dircn]=spp(t,x,flag,f)

Usually, while calling ode45, something like this would work if spp did not have a flag argument.

options=odeset('RelTol',1e-13,'AbsTol',1e-14,'events','on');
[t,x,te,xe,ie]=ode45(@(t,x)spp(t,x,f),[0 2*pi/OMEG],[xin;xdin],options);

I have searched around but cannot find the solution. Please help me out.

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I do not exactly know how to treat 'flags' but usually when I need to pass extra variables to the ode I define them as 'global' in the main .m file and also in the file where I define the function I give to the ode.

Or you might use the varargin function .

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  • $\begingroup$ Yes, that did the trick. $\endgroup$
    – zynga
    Nov 8 '14 at 16:49
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Why don't you simply pass flag the way you are passing f?

[t,x,te,xe,ie]=ode45(@(t,x)spp(t,x,flag,f),[0 2*pi/OMEG],[xin;xdin],options);

(Global variables in MATLAB often cause problems and it is best to avoid them, if possible.)

Maybe I'm missing something here?

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  • $\begingroup$ flag is not a variable I am allowed to pass. The value of flag is decided by ode45 function at every iteration. $\endgroup$
    – zynga
    Nov 8 '14 at 16:15
  • $\begingroup$ Are you talking about "flag" in the ode output function? The output function is not the same function as the "odefun." You have not defined an output function. $\endgroup$ Nov 8 '14 at 16:20
  • $\begingroup$ No, I am not using an output function. I am using flag as an argument to a user defined function, the value of which will be updated by ode45. I think it is allowed. $\endgroup$
    – zynga
    Nov 8 '14 at 16:51

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