# Error While running a while loop (index exceeds number of array elements)

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Mia Loposser on 26 Oct 2020 at 0:51
Edited: Cris LaPierre on 26 Oct 2020 at 16:27

#### 1 Comment

Mia Loposser on 26 Oct 2020 at 1:35
clear
close
%givens
E0 = 3; %input voltage
ls = 7*10^-14; %value of ls
R = 200; %value of resistor
C = .026; %value of KT/q
V_vec = [];
Vdiode(1) = 1; %initial guess for Vdiode
Vdiode(2)= 2;
i=1;
%iterate until difference between last 2 Vdiodes < 10^-6
while abs(Vdiode(i + 1) - Vdiode(i)) > 10^-6
% derivative of f
fprime = -1-ls*R/C * exp(Vdiode(i)/C);
% f at Vdiode
f = E0 - Vdiode(i) - ls * R * (exp(Vdiode(i)/C) - 1);
% new Vdiode
Vdiode(i) = Vdiode(i) - f/fprime;
% store in vector
V_vec(i) = Vdiode(i);
% increment i
i = i + 1;
end
Vdiode
length(V_vec)

Cris LaPierre on 26 Oct 2020 at 1:00
Edited: Cris LaPierre on 26 Oct 2020 at 16:27
You create variable Vdiode so that it contains a single value, 1. Then in your while condition, you try to compare the second value with the first. There is no second value, resulting in the error you see. I've transcribed the relevant parts of your code below and run it so you can see.
clear
Vdiode(1) = 1
Vdiode = 1
Vdiode(2)
Index exceeds the number of array elements (1).

Mia Loposser on 26 Oct 2020 at 1:33
thank you for your help! sorry about that. after adding a value for Vdiode(2) i am still recieving the error message:
index exceeds the number of array elements (2)
Cris LaPierre on 26 Oct 2020 at 2:14
This is going to be a cyclical issue until you fix the underlying logic. Step through your code one loop at a time. There is an error around either when you increment i, or which two values you compare (right now you are including the next value. Perhaps you want to look at the previous value instead? This means (i-1) and i).

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