Sum of different Matrix elements

I've tried to look around to see if there were answers to my question, but I'm not sure how to word it. Hopefully you guys understand what I mean.

I'm trying to make a Gauss-Seidel iterative algorithm. My problem is when trying to find x sub i to the (k+1):

I'm not sure how to to take individual elements of a vector and compute them in a for loop given we have matrices "a" and "b".

[Sean Murphy]

I've continued to look for information, but I am still lost in the sauce.

[ChristianW]

Link not working and bad explained. What does this mean: trying to find x sub i to the (k+1)?

Here is the sum of Matrix element 1 and 2.

M = [1 3; 2 4];
M(1)+M(2)

[Sean Murphy]

Hopefully the equation will give some insight. Im just unsure how to take any of the summations with matrix indexing. I've tried my best to explain it.

Thanks.

Answer 1

[Matt J]

I'm not sure how to to take individual elements of a vector

For example,

a(i,1:n-1)