Applying higher value of input parameter for some interval input variable in ODE.

N=10;
k=zeros(N,1);
r=zeros(N,1);
t=zeros(N,1);
k1=1;k(1)=1;t(1)=0;dt=0.05;
for i=2:N
    t(i)=t(i-1)+dt;
    k(i)=k1;
    r(i)=r(i-1)*dt+k(i);
     if r(i)<5
         % I want to apply higher value of k i.e. k1+1 for some
         % interval of time before and after t(i) at which r(i) is equal to 0.5. 
         %  For example if t(i)=10 for r(i)=0.5, then
         % I want to use higher value of k in the time range of 5 to 15.
         k(i)=k1+1;
            r(i)=r(i-1)*dt+k(i);
     end
end
plot(t,r)