For loop that runs until value reaches a certain point.

I am trying to work this program to produce the k_eff and phi_eff that meet the conditions below but don't know what is wrong with the code.

A =

0.1139 -0.0139 0 0 0 0

-0.0069 0.1139 -0.0069 0 0 0

0 -0.0069 0.1139 -0.0069 0 0

0 0 -0.0069 0.1139 -0.0069 0

0 0 0 -0.0069 0.1139 -0.0069

0 0 0 0 -0.0139 0.2806

F =

0.1240 0 0 0 0 0

0 0.1240 0 0 0 0

0 0 0.1240 0 0 0

0 0 0 0.1240 0 0

0 0 0 0 0.1240 0

0 0 0 0 0 0.1240

Both F and A are 6x6 matrices

k initial or k_o = 1

phi initial or phi_o = ones(N+1,1)

N=5

crit_k=10^-9;
crit_phi=10^-8;
N=5;
    
for i=1:1:inf
   
    k_o=1;
    phi_o=ones(N+1,1);
    
    if (i-1)==0
       k=k_o;
       phi=phi_o;
        
    else
    
    phi(i)=A\((1/k(i-1))*F*phi(i-1));
    
    k(i)=k(i-1)*sum(phi(i))/sum(phi(i-1));
    
         if abs(k(i)-k(i-1))/k(i)<=crit_k && abs(phi(i)-phi(i-1))/phi(i)<=crit_phi
             k_eff=k(i);
             phi_eff=phi(i);
             break;
         end
     
    end
end

[Image Analyst]

Evidently your criteria is never met. Why don't you plot the ratio at each iteration and see what it does?

Don't use a for loop with an infinite number of iterations. Use a while loop instead, and don't forget to have one condition be a check on the number of iterations so that it doesn't get unreasonably large.