Persistent Variable in a Function

Hi,

I'm having difficulty writing code for a persistent variable. The goal is to have a value either be 1 or 0, depending on velocity. If velocity goes under 5 m/s, the function "turns on", effectively adding the component of the equation it is attached to, for 10 seconds. After that 10 seconds, it should automatically be reset to zero to "turn off" that particular part of the equation. Here is the equation in the script:

F = @(v,t) -((b/mc)*v.^2)-(9.81)*sin(theta)+(Fg/mc)*abs(sin(freqg*t))-(Fb/mc)*abs(sin(freqb*t))+(Fr/mc)*Rect(v,t);

Rect(v,t) is the function containing the persistent variable, and here is what I have so far:

function [ j ] = Rect( v,t )
  if Check(v)<5
    for t=t:1:t+10
      j=1;
    end
  else
    j=0;
  end
end

I'm having difficulty wrapping my head around how to code it to behave how I would like it to. Any help is appreciated, thank you!

[dpb]

What is Check intended to be? It's undefined in the function unless it's a GLOBAL (ugly!).

[Josh Cheng]

it's intended to check the velocity, but if there's a better way I'm all up for it!

Answer 1

[Guillaume]

Most likely, you would be better off without that Rect subfunction and instead use a variable to track the state of that Rect inside the loop that calls F.

Failing that, the following Rect would work:

function state = Rect(v, t)
   persistent triggertime;
   if v < 5
      %add t to the list of trigger times
      triggertime = [triggertime t]; %#ok<AGROW>
   end
   state = any(t >= triggertime & t < triggertime + 10);
end

[Josh Cheng]

Thank you, that worked wonderfully!