Array Indices must be positive integers or logical values - problem

Hello guys, so I am trying to run this code that I have attached but in the final portion (lines 56-59) I am getting the error "array indices must be positive integers or logical values." What is happening here?

clc
clear all

%% Problem 1
thermoCouple = 1:1:7;
zeroHz = [73.35 72.59 71.58 70.05 68.11 64.04 60.86];
fiveHz = [60.78 58.58 55.64 51.33 45.81 35.24 28.29];
fifteenHz = [57.50 55.20 52.18 47.75 42.70 32.78 27.36];
twentyfiveHz = [54.28 51.85 48.75 44.28 39.80 29.89 25.32];

freeStreamT0 = 24;
freeStreamT5 = 24.2;
freeStreamT15 = 23.2;
freeStreamT25 = 24.3;
i = 1;

for i = 1:7
    calcTemp0(i) = (zeroHz(i)-freeStreamT0)/(80-freeStreamT0); 
    calcTemp5(i) = (fiveHz(i)-freeStreamT5)/(80-freeStreamT5);
    calcTemp15(i) = (fifteenHz(i)-freeStreamT15)/(80-freeStreamT15);
    calcTemp25(i) = (twentyfiveHz(i)-freeStreamT25)/(80-freeStreamT25);
end

% Constant Area Fin Boundary Conditions
length = 0.292;
thermoCoupleLengths = [0.009 0.02 0.03 0.05 0.08 0.15 0.29];
k = 167;
diameterFin = 0.025;
pf = diameterFin * pi;
ac = (pi * (diameterFin^2))/4;
PFree = [0.1 1 9.9 29.5];

for i = 1:4
    PFreePa(i) = PFree(i)*9.80665;
end
for i = 1:4
    VFree(i) = sqrt((PFreePa(i)^2)/1.225);
end
for i = 1:4
    Re(i) = (VFree(i)*0.25)/(1.81*10^-5);
end
Pr = 0.71;
for i = 1:4
    Nu(i) = 0.3 + (0.62*(Re(i)^(1/2))*(Pr^(1/3)))/((1+(0.4/Pr)^(2/3))^(1/4))*((1+(Re(i)/282000)^(5/8))^(4/5));
end
for i = 1:4
    h(i) = (Nu(i)*k)/diameterFin;
end
for i = 1:4
    m(i) = sqrt((h(i)*pf)/(k*ac));
end
mu = m(4);
he = h(4);

for i = 1:7
    convectionCase(i) = (cosh(mu*(length-thermoCoupleLengths(i)))+(he/(mu*k))*sinh(mu(length-thermoCoupleLengths(i))))/(cosh(mu*length)+(he/(mu*k))*sinh(mu*length));
    adiabaticCase(i) = (cosh(mu*(length-thermoCoupleLengths(i))))/cosh(mu*length);
    prescribedCase(i) = (((twentyfiveHz(i)-freeStreamT0)/80-freeStreamT0)*sinh(mu*thermoCoupleLengths(i))+sinh(mu*(length-thermoCoupleLengths(i))))/sinh(mu*length);
    infiniteCase(i) = e^-(mu*thermoCoupleLengths(i));
end

Array indices must be positive integers or logical values.

Answer 1

[Image Analyst]

See the FAQ for a thorough discussion

https://matlab.fandom.com/wiki/FAQ#%22Subscript_indices_must_either_be_real_positive_integers_or_logicals.%22

Don't use length as your variable name. That is the name of a built-in function.

mu is a scalar not an array so you can't do

convectionCase(i) = (cosh(mu*(length-thermoCoupleLengths(i)))+(he/(mu*k))*sinh(mu(length-thermoCoupleLengths(i))))/(cosh(mu*length)+(he/(mu*k))*sinh(mu*length));

perhaps you meant

convectionCase(i) = (cosh(mu*(length-thermoCoupleLengths(i)))+(he/(mu*k))*sinh(mu*(length-thermoCoupleLengths(i))))/(cosh(mu*length)+(he/(mu*k))*sinh(mu*length));