# How to pass a function handle of an anonymous function into ode45 function in matlab?

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Amr Tolba 2014 年 6 月 9 日

I need to pass an inline anonymous function into ode45 function in matlab but i have not managed to to that. I have looked through the help of matlab but didn't help me. let's give a code example to clarify:
I have a matrix function as follows: f_xyz = @(x,y,z) [-1 1 0;2 -1 -x;0 y -3]*[x;y;z];
and i would like to pass it into ode45 function with such syntax:
[T Y] = ode45(ode_function,time_interval,initial_values);
I checked many forums to get some hints but i didnt work please advise me how to do that?
P.S. :I know how to do that if we have a m-file function but i need it to be as an anonymous function.

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### 回答 (1 件)

Cedric Wannaz 2014 年 6 月 9 日

Assuming that your problem has 3 dimensions, so you have for example
x0 = [10; 5; 7] ; % [x1(0), x2(0), x3(0)], or
% [x(0), y(0), z(0)] with your notation.
where 10 is the initial condition for dim 1, etc, ODE45 will call the function f that it receives as 1st arg, referenced by its handle @f, with the following parameters:
f( t, x, ... )
where ... symbolize extra parameters that can be defined as extra parameters in the call to ODE45, or through an appropriate definition of the function/handle that you pass as 1st argument. You have therefore to pass a function which takes t and x in this order. If you have the freedom to define f_xyz, you should then define it as follows
f_xyz = @(t, x) [-1 1 0;2 -1 -x(1);0 x(2) -3] * x ;
If you cannot modify f_xyz, you can pass a handle on an intermediary anonymous function which plays the role of interface, adjusting parameters orders/structure:
% f_xyz defined elsewhere, you cannot access/modify it.
f_xyz = @(x,y,z) [-1 1 0;2 -1 -x;0 y -3]*[x;y;z];
% Call to ODE45 using an "interface" anonymous function.
[t, x_t] = ode45( @(t, x) f_xyz(x(1), x(2), x(3)), ... ) ;
Note that you can give a name to this interface function if you prefer not to deal with anonymous functions (but you'll often see people using anonymous functions here)..
interf = @(t, x) f_xyz(x(1), x(2), x(3)) ;
[t, x_t] = ode45( interf, ... ) ;
Hope it helps

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