why the time "t" inside the ode solver OutputFcn is not a scalar?

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Ehsan Asadi 2014-12-18

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/167020-why-the-time-t-inside-the-ode-solver-outputfcn-is-not-a-scalar

编辑： Geoff Hayes 2014-12-20

For an ODE problem that I have, I need to evaluate some values right after each successful ODE step. therefore I decided to use OutputFcn (output function that is supposed to run only successful steps). I wrote a code and here is its summay:

options =odeset('OutputFcn',@My_OutputFcn,));
[T,Y]=ode15s(@ode_func,[simulation_time_start,simulation_time_end],initial_conditions,options]

%%%%%%%%%%%%%%%%%

where the OutputFcn is:

function status = My_OutputFcn(t,y,flag,varargin)
global force
t
force= force+t;

%%%%%%%%%%%%%

but the problem is that in the above method, sometimes the parameter t (time) is a vector rather than being a scalar. Why is that happening and how to fix it?

I am printing "t" in the middle of My_OutputFcn and here is a copy of the command window:

t =
           0    0.1500
t =
      0.0050
t =
      0.0100
t =
      0.0150
t =
      0.0200
t =
      0.0250
t =
      0.0300
t =
      0.0350
t =
      0.0400    0.0450
t =
      0.0500
t =
      0.0550    0.0600