How fix this GaussPivot code, since I got a nonsense results for this specific a, b matrix?

unction x = GaussPivot(a,b)
format long 
% The function solves a system of linear equations ax = b using the Gauss
% eliminaion mehod with pivoting
ab = [a,b];
[R, c] = size(ab);
for j = 1:R-1
    % Pivoting block
    if ab(j,j) == 0
        for k = j +1:R
            if ab(k,j) ~=0
                abTemp = ab(j,:);
                ab(j, :) = ab(k,:);
                ab (k,:) = abTemp;
                break
            end
        end
    end
    % Pivoting block ends
    for i = j+1:R
        ab(i,j:c) = ab(i,j:c)-ab(i,j)/ab(j,j)*ab(j,j:c);
    end
end
x = zeros(R,1);
x(R)= ab(R,c)/ab(R,R);
for i= R-1:-1:1
    x(i) = (ab(i,c) -ab(i,i +1:R)*x(i+1:R))/ab(i,i);
end

and a and b matrix

a = [0 0.9231 0 0 0 0 0 0; -1 -0.3846 0 0 0 0 0 0; 0 0 0 0 1 0 0.8575 0;
    1 0 -0.7809 0 0 0 0 0; 0 -0.3846 -0.7809 0 -1 0.3846 0 0;
    0 0.9231 0.6247 0 0 -0.9231 0 0; 0 0.6247 -1 0 0 0 0 0;
    0 0 0 1 0 0 -0.5145 -1];
b = [1690;3625;0;0;0;0;0;0];
Forces  = GaussPivot(a,b)