ODE45 function time step

Hi,

How can i increment a global variable in every time step of the ode45 function or in other words each sampling time of the ode45 function

thank you

Answer 1

[Jan]

Avoid using global variables, because they are a shot in your knee.

Use a persistent variable instead and reply it to the caller for specific input arguments.

You cannot implement this in the function to be integrated, because the solver might reject some steps. So use the OutputFcn, which is called after successful steps only.

[Anis Frej]

Thank you for your answer

Can you give me an example ?

[Jan]

See: https://www.mathworks.com/help/matlab/ref/odeset.html#d123e928217

options = odeset('OutputFcn', @YourOutput);
[t, y] = ode45(@YourODE, tSpan, y0, options);

function status = myOutputFcn(t,y,flag)
persistent Data
if isempty(Data)
    Data.t = [];
    Data.y = [];
end

status = 0;
switch flag
    case 'init'
        Data = [];
        
    case 'done'
        
    case []
        Data.t(end + 1)    = t;
        Data.y(end + 1, :) = y;
        
    case 'flush'
        status = Data;
        
    otherwise
        error('Bad flag');
end
end

Now run the integration and obtain the current status by:

Data = myOutputFcn([], [], 'flush')

[Anis Frej]

Thank you very much