How to rectify the error - 'Subscript indices must be real positive integers or logicals' for the code below

%...My Code T.F=[(68659K)s^2+(68659K*a+243740K)s+243740Ka]/[s^3+(68659K+68743)s^2 +
%(243740K+246675+68659K*a)s + (46120+243740k*a)]

clf;
t=0:0.01:5;
k=0;
for i = 1:49;
    K(i)=51-i*1;
    for j = 1:40;
        a(j)=2.05-j*0.05;
        num=[0 68659*K(i) 68659*K(i)*a(j)+243740*K(i) 243740*K(i)*a(j)];
        den=[1 68743+68659*K(i) 68659*K(i)*a(j)+243740*K(i)[phone]+243740*K(i)*a(j)];
        y=step(num,den,t);
        m=max(y);
        s=501;while y(s)>0.98 & y(s)<1.02;
            s=s-1;end;
        ts=(s-1)*0.01;
        if m<1.10 & m>1.02 & ts<3.0;
            k=k+1;
            table(k,:)=[K(i) a(j) m ts];
        end
    end
end
table(k,:)=[K(i) a(j) m ts]

Answer 1

[Walter Roberson]

Posting the line that the problem is occurring on helps us to track down the problem.

In your code

while y(s)>0.98 & y(s)<1.02;
          s=s-1;end;

you will underflow s to 0 if all of the y satisfy that condition.

[shahid]

The error in my code is indicated at the last line- table(k,:)=[K(i) a(j) m ts] I will also like to add that i have successfully run the above code logic for a different transfer function i.e the only difference was in stating num and den.But for the above transfer function i am not getting the desired results. Hope I have made myself clear

[Walter Roberson]

Your "k" starts out 0, and is only increased under a fairly limited set of conditions. But then at the end you try to assign to table(k,:) when k might still be 0.

[shahid]

So what should I do Mr. Walter Roberson ?

[Walter Roberson]

What do you want to have happen in that situation? And what values are you expecting "i" and "j" to have after the end of the nested for loop?