How do I fix index, I keep getting an error

function x = Gauss2(A,b);
% Solve linear system Ax = b
% using Gaussian elimination without pivoting
% A is an n by n matrix
% b is an n by k matrix (k copies of n-vectors)
% x is an n by k matrix (k copies of solution vectors)
A=[1 0 0 0 0 0 -1 0, 0 -1 0 -1 0 0 0 0, 0 1 -1 0 0 0 0 0, 1 0 0 1 -1 0 0 0, 0 0 0 0 1 1 0 0, 0 0 1 0 0 1 0 0, 0 0 0 0 0 0 -1 0, 0 0 0 0 0 0 1 -1]
b= [35 -50 30 40 20 60 -90 25]'

[n, n] = size(A);     % Find size of matrix A
[n, k] = size(b);     % Find size of matrix b
x = zeros(n,k);      % Initialize x
for i = 1:length(n)
    m = -A(i+1:n,i)/A(i,i);
    A(i+1:n,:) = A(i+1:n,:) + m*A(i,:);
    b(i+1:n,:) = b(i+1:n,:) + m*b(i,:);
end;

% Use back substitution to find unknowns
x(n,:) = b(n,:)/A(n,n);
for i = n-1:-1:1
    x(i,:) = (b(i,:) - A(i,i+1:n)*x(i+1:n,:))/A(i,i);
end

Answer 1

[Walter Roberson]

When you created A, you used commas. Change those commas to semi-colons. Your current A is a vector instead of a 2D array.

[David Velo]

Matrix A is supposed to be an 8X8 matrix

[Walter Roberson]

Your line

A=[1 0 0 0 0 0 -1 0, 0 -1 0 -1 0 0 0 0, 0 1 -1 0 0 0 0 0, 1 0 0 1 -1 0 0 0, 0 0 0 0 1 1 0 0, 0 0 1 0 0 1 0 0, 0 0 0 0 0 0 -1 0, 0 0 0 0 0 0 1 -1]

creates a row vector. The line

A=[1 0 0 0 0 0 -1 0; 0 -1 0 -1 0 0 0 0; 0 1 -1 0 0 0 0 0; 1 0 0 1 -1 0 0 0; 0 0 0 0 1 1 0 0; 0 0 1 0 0 1 0 0; 0 0 0 0 0 0 -1 0; 0 0 0 0 0 0 1 -1]

would create an 8 x 8 array, as would

A= [1 0 0 0 0 0 -1 0
    0 -1 0 -1 0 0 0 0
    0 1 -1 0 0 0 0 0
    1 0 0 1 -1 0 0 0
    0 0 0 0 1 1 0 0
    0 0 1 0 0 1 0 0
    0 0 0 0 0 0 -1 0
    0 0 0 0 0 0 1 -1]

Space between items on the same line is the same as comma between items on the same line: it is for creating columns in the same row. Semicolon between parts breaks up into rows. Newline without ... operator also breaks into rows.