Sttopping the iteration at a certain value

HI!

I have a vector length of 0:0.1:1 and ineed iteration according to this vector length. I have done this part now i need to stop these iteration when valuee of r becomes positive but it doesnt work what should i do.Hve a look on this code.I need the loop to break when real part of poles that is r (any of three values in vectoor) becomes +ive but it doesn;t work.The condition work perfectly for r<0 condition but not for this.plzz help

for k= 0:0.1:1 
  n=conv(k,[0.5 1.3]);
  d=[1 1.2 1.6 0];
   sys1=tf(num1,den);
    P=pole(F);
     r=real(P)
     if r>0
         break 
     end
end

Answer 1

[Star Strider]

The ‘F’ variable is apparently defined before the loop and does not appear to be changed within the loop. Therefore, ‘r’ never changes and the if condition is never satisfied.

[Tina]

But if i do that then the systen won't know what r is .

and it works for following condition

 if r<0
         break 
     end

[Star Strider]

The point is that ‘F’ is not calculated within the loop and so by definition never changes within the loop, and so ‘r’ never changes within the loop. If before the loop, it will remain so within the loop.

[Tina]

 for k=1:0.1:2
     n=conv(k,[0.5 1.3]);
      d=[1 1.2 1.6 0];
     sys1=tf(num1,den)
   if r>0
       
     F=feedback( sys1,1);  P=pole(F);
     r=real(P)
         break 
     end
    
  end

if this is what you are talking about,then the matlab doesnt respond and code doesn.t work

[Star Strider]

That is significantly different from the code you originally posted!

There is not enough information provided to run this code as well.

The order of the statements appears to test ‘r’ before it is calculated. Assuming ‘r’ is defined somewhere prior to the loop, it would test on the preceeding value of ‘F’ and output the subsequent value of ‘F’.

It could very easily be that your system is causal and stable and all the poles remain in the left-half plane, so the test will always fail.

[Tina]

 for k=2:0.1:3
     n=conv(k,[0.5 1.3]);
      d=[1 1.2 1.6 0];
     sys1=tf(1,d)
     F=feedback( sys1,1)
     P=pole(F);
     r=real(P)   
     if r<0 
 
     else
      
          break 
       
     end
    

So this is the code to find the stability of transfer function with the increase of k values.So when I use the code ,it works but it still dispay the values when the system become unstable and then breaks.Like now it's only displaying the value at which it become unstable .is it possible that it doesn't even show that one value too?

[Star Strider]

The earlier if block made more sense.

It should show all the ‘F’ systems until it breaks. (It isn’t configured to store any of them, however.)

If you want to save them to use later, try this:

k=2:0.1:3;
for kk = 1:numel(k)
    n=conv(k(kk),[0.5 1.3]);
    d=[1 1.2 1.6 0];
    sys1=tf(1,d)
    F=feedback( sys1,1)
    Fsave{kk} = F;
    P=pole(F);
    r=real(P)
    if r>0
        break
    end
end

I’m still not certain what the problem is.

[Tina]

OK THANKS

[Star Strider]

As always, my pleasure!