Why isn't this if statement nested in a for loop working?

I am trying to use fuel consumption, velocity, and time data from a real-world drive cycle to calculate the fuel consumed during idle (vehicle speed = 0). IdleFuel represents the volume of fuel consumed during idle; so when vehicle speed =/= 0, IdleFuel should be zero. Here is some sample data and my code (I simplified my actual data, for brevity):

   % Time (s)
    time = [0 1 2 3 4 5];
    % Fuel consumed (L)
    Fuel_Consumed = [0.5 1 1.5 2 2.5 3];
    % Vehicle speed (mph)
    VSPD = [0 10 20 0 10 20];

    IdleFuelIndex = find(VSPD == 0); %(find indexes where VSPD = 0)
    IdleTime = time(IdleFuelIndex); %s (times when VSPD = 0)
    IdleFuel=0;
    for n = 1:length(time)
        if n == IdleFuelIndex
            IdleFuel(n) = Fuel_Consumed(n);
        else IdleFuel(n) = 0;
        end
    end

When I run this, I just get that IdleFuel=0...why is this? I think Matlab is having trouble recognizing what to do if the vehicle speed returns to zero after being nonzero; when I tried altering the data such that only the first entry in the VSPD vector was zero, it seemed to work...but if it returns to zero (such as the fourth entry in the VSPD vector), it just returns IdleFuel as 0. How can I fix this??

Thank you for your time!

Answer 1

[Chad Greene]

It doesn't work because n (a scalar) will never equal IdleFuelIndex (a vector).

[Kelsey]

 Thanks for your response! How can I say "for every time n equals some entry in the vector"?

[Kelsey]

Update...I tried this:

% Time (s)
time = [0 1 2 3 4 5];
% Fuel consumed (L)
Fuel_Consumed = [0.5 1 1.5 2 2.5 3];
% Vehicle speed (mph)
VSPD = [0 10 20 0 10 20];

IdleFuelIndex = find(VSPD == 0); %(find indexes where VSPD = 0)
NonIdleFuelIndex = find(VSPD ~= 0);
IdleTime = time(IdleFuelIndex); %s (times when VSPD = 0)
NonIdleTime = time(NonIdleFuelIndex); %s
IdleFuel=0;

NonIdle = ismember(time,NonIdleTime);
Idle = ismember(time,IdleTime);
for n = 1:length(time)
    if Idle(n) = 0                            %(if not idle)
        IdleFuel(n+1) = 0;
    elseif Idle(n) = 1                        %(if idle)
        IdleFuel(n+1) = Fuel_Consumed(n+1);
    end
end

though I'm still getting errors...any ideas?

[Chad Greene]

You need a double equals in these lines:

if Idle(n) == 0                            %(if not idle)

and

    elseif Idle(n) == 1                        %(if idle)