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

[Mia Loposser]

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)

Answer 1

[Cris LaPierre]

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]

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]

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).