Impose to a vector not to have zero elements

Hi everybody I need an help. Actually I've got a problem with my matlab code. The code is quite long and complex and deals with autonomous driving. I made a control system such that a leader vehicle tells to other vechicles behind to follow it. Now, i would like that, given an acceleration law, my vector that contains the speed does not become zero, or lower, in case of a high deceleration. How can I perform this?

speed=zeros(N,size(sol.y,2)); 
speed(1,:)=sol.y(N+1,:);
speed(2,:)=sol.y(N+1,:)-sol.y(N+2,:);
for n=3:N
    speed(n,:)=sol.y(N+1,:)-sum(sol.y(N+2:N+n,:),1);
end

that is how my speed vector, for each vehicle is filled up...But, regardless from this, how can I say to matlab "if speed <=0 then speed=0?

thanks

Answer 1

[Dana]

speed(n,:)=max(sol.y(N+1,:)-sum(sol.y(N+2:N+n,:),1), 0);