Array indices must be positive integers or logical values.

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Alastair Combe 2019-4-11

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https://ww2.mathworks.cn/matlabcentral/answers/455729-array-indices-must-be-positive-integers-or-logical-values

评论： Alastair Combe 2019-4-12

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

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Torsten 2019-4-11

Maybe I is never 3 ? Or t1 and t2 don't have the same length as I ? We don't know.

Alastair Combe 2019-4-11

There was a problem with that as well, i put 3 in to stop an error occuring there as well, it was originally 1. it creates

> I==1
ans =
  500×1 logical array
  I==3
ans =
  500×1 logical array

The only difference is that I==1 creates some 1's and 0's in the array as opposed to I==3 creates a list of only 0's

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Answer 1

Guillaume 2019-4-11

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https://ww2.mathworks.cn/matlabcentral/answers/455729-array-indices-must-be-positive-integers-or-logical-values#answer_370155

在 MATLAB Online 中打开

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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Alastair Combe 2019-4-12

function [V,P,G,WE,D,t] = calc_acceleration(nds,rho,cd,A,m,s,Rw,V0)
ni = [13.506352;
    10.34140225;
    9.606723481;
    7.908904582;
    6.739277848;
    5.762254242;
    5.042848362;
    4.468644723];
V = zeros(nds,1);
P = zeros(nds,1);
G = zeros(nds,1);
WE = zeros(nds,1);
D = zeros(nds,1);
gear = 1;
ds = s(2)-s(1);
t = zeros(nds,1);
gchange_time = 0.001;
tsgc = 0;
% Loop
for i=1:nds
    dt = ds/V0;
    
    % Calculate drag
    D = 0.5*rho*cd*(V0^2)*A;
    
    % Choose gear and get power
    if tsgc < gchange_time
        power = getPower((ni(gear)*V0)/Rw);
        tsgc = tsgc + dt;
    else
        power = zeros(numel(ni),1);
        for g=1:numel(ni)
            power(g) = getPower((ni(g)*V0)/Rw);
        end
        [power,newgear] = max(power);
        if newgear ~= gear
            tsgc = 0;
        end
        gear = newgear;
    end
    
    We = (ni(gear)*V0)/Rw;
    WE(i) = We;
    P(i) = power;
    G(i) = gear;
    
    % Calculate torque at wheel
    Te = (power/We)*0.85;
    Tw = Te*ni(gear);
    
    %Add wheel inertia
    
    WI = 4*(10*(0.335)^2);
    
    % Calculate net force
    Fw = (Tw+WI)/Rw;
    F = Fw-D;
    
    % Calculate acceleration
    a = F/m;
    
    % Calculate new veloicty
    V(i) = V0;
    V0 = sqrt(V0^2 + (2*a*ds));
    if i>1
        t(i) = t(i-1) + dt;
    end
    
end
end

This is calc_acceleration

Torsten 2019-4-12

编辑：Torsten 2019-4-12

calc_acceleration has 6 outputs while your call to calc_acceleration only uses five of them.

Use

[Va,P,G,WE,~,t1] = calc_acceleration(nds,rho,cd,A,m,s,Rw,cnrVel(pcn));

instead of your call.

Alastair Combe 2019-4-12

That was it, it's running now and producing a time. Thanks very much!

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Array indices must be positive integers or logical values.

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