Error in plotting (blank graph): Vector Size

v--- = linspace(0,35,36);
v = v * 0.44704;
N = length(v);
for i= 0:N
    if (i < 30)
        eta(i+1) = -0.001778 * ((v(i+1)).^2) + 0.05333 * (v(i+1));
    else
        eta(i+1) = 0;
    end
end

hold on
plot (v,eta,'r-')
xlabel('Speed (m/s)')
ylabel('Net Efficiency (Percent)')
hold off

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I have pasted my code above. When I go to plot the data (v on x axis, eta on y axis), it says there is an error and that the vectors must be the same length. Any suggestions for a fix?

Answer 1

[Ameer Hamza]

Check the following code. You don't need to use eta(i+1).

v = linspace(0,35,36);
v = v * 0.44704;
N = length(v);
eta = zeros(1, N); % pre-allocation for efficiency
for i= 1:N
    if (i < 30)
        eta(i) = -0.001778 * ((v(i+1)).^2) + 0.05333 * (v(i+1));
    else
        eta(i) = 0;
    end
end
hold on
plot (v,eta,'r-')
xlabel('Speed (m/s)')
ylabel('Net Efficiency (Percent)')
hold off

Answer 2

[madhan ravi]

No loops needed:

eta = -0.001778 * v.^2 + 0.05333 * v;
eta(30 : end) = 0;