MATLAB: Array indices must be positive integers or logical values.

automotiveformula 1integrationtimings

I am writing a program to simulate an F1 car laptime. Imagibe the car has come out of a corner and is accelerating doen a straight until it has to brake for the next corner. The times for this acceleration and deceleration have to be counted seperately as they are governed by seperate functions. There is a part of the code where the time taken to accelerate on a staright (t1) has to be reset to 0 to then start the the clock for the time taken to decelerate for the upcoming corner (t2) to be counted. I keep getting the same error "Array indices must be positive integers or logical values." no matter what i do.
% Calculate the straights
strTimes = zeros(num_str,1);
sLap = zeros(nseg*nds,1); %sLap = distance around lap
vCar = zeros(nseg*nds,1); %vCar = velocity of car around lap
str = 1;
smax = 0;
for i=1:nseg
    rad = track(i,2);
    dist = track(i,1);
    s = linspace(0,dist,nds)'; %nds = 500 (no. of iterations)
    nstart = ((i-1)*nds+1);
    nend = (i*nds);
    sLap(nstart:nend) = smax + s;
    smax = max(sLap);
    
    % Straight
    
    if rad == 0
        ds = s(2)-s(1);
        
        % Corner segment numbers
        
        pcsn = i-1; %previous corner segment number
        ncsn = i+1; %next corner segment number
        if pcsn < 1
            pcsn = max(cnrNum);
        end
        if ncsn>nseg
            ncsn = min(cnrNum);
        end
        
        pcn = find(pcsn==cnrNum);
        ncn = find(ncsn==cnrNum);
        
        [Va,P,G,WE,t1] = calc_acceleration(nds,rho,cd,A,m,s,Rw,cnrVel(pcn));
        [Vd,t2] = calc_deceleration(ds,cnrVel(ncn),nds,rho,A,cd,m,cz);
        
        [V,I] = min([Va,Vd],[],2);
        vCar(nstart:nend) = V;
        
        % Reset the clock for the braking time, ncn = next corner number
        %cnrVel = corner velocity, t1 = acceleration time
        %t2 = deceleration time
  
        if max(V) > cnrVel(ncn) 
            ta = t1(I==3);
            tb = t2(I==3);
            tb = tb+(ta(end)-tb(1));
            t = [ta;tb];
        else
            t = t1;
        end
        
        strTimes(str) = max(t);
        
        str = str+1;
    else
        vCar(nstart:nend) = ones(nds,1)*cnrVel(i==cnrNum);
    end
end

Best Answer

They're not meant to be empty
Well, then you go back through the code to find out why they're empty.
Going up we see,
ta = t1(I==3);
So clearly if I doesn't contain 3 exactly, ta will be empty. So what is I?
[V,I] = min([Va,Vd],[],2);
It's the colum index where a minimum is found. I don't know what Va and Vd are. if they are column vectors then [Va, Vd] only has two columns, and obviously, you're never going to find a minimum in the 3rd column. If Va and or Vd have more than one column, the the minimum could be found in column 3 but there is absolutely no guarantee of that.
As it is, either you're guaranteed they're empty (if Va and Vb both have only one column) or they could be empty if no row of [Va, Vb] has its minimum in the 3rd column.
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