Index exceeds the number of array elements (1).

Hi, I am getting the same error as in the tittle. I am very new to coding and I do not know why I am getting it. I tried stepping through the code and it gets stuck on, i=3 b=3. Please help. My code is below and the alpha matrix is the attached picture. Furthermore, you can think of g(M) as just a constant. Thanks to everyone who helps! :D

a(1)=g(M);
for i=2:M
    su = 0;
    v(1) = 1; 
    for b=2:i
        su =su - alpha(b, b-1)*v(b-1);
    end
    a(i)=g(M)*su;
end
a=fliplr(a);

Answer 1

[Walter Roberson]

You initialize v(1) only, and no other v.

You use v(b-1) in the loop, which requires that you have more v available, such as if you were to be assigning to v(b) inside the for b loop.

[Bradley Kitzul]

Hi, thank you for the response! Do you have any suggestions on how to fix this issue?

[Walter Roberson]

When b becomes 3, so that v(b-1) is trying to access v(2), then what do you expect that v(2) value to be? Do you expect it to be something you had already initialized before the loop, or do you expect it to be something that you calculated during the previous iteration of the for b loop? If you are extending v as you go, then what is the formula for the new v ?

[Bradley Kitzul]

Here are the equations I am trying to implement. So yes it is calculated in the previous loop. Sorry if my question is rudimentary, I am new to this stuff! :D

Answer 2

[Walter Roberson]

Code it using the same variables as in the equations, or else you are going to get yourself confused.

v(i) = 1;
for m = i+1:M
    v(m) = - sum(alpha(m, i:m-1) .* v(i:m-1));
end
a(i) = sum(g(i:M) .* v(i:M));

[Bradley Kitzul]

Thank you!