Why do I get this error for my gauss seidel code?

a = [3 -.1 -.2; .1 7 -.3; .3 -.2 10];
b = [7.85; -19.3; 71.4];
x = [0;0;0];
imax = 10;
es = 1e-6;
lambda = 0.5;
n = 3;

for i = 1:n
    dummy = (a(i,i))
    for j = 1:n
        a(i,j) = a(i,j)/dummy
    end
    b(i) = b(i)/dummy
end
for i = 1:n
    sum = b(i)
    for j = 1:n
        if i ~=j
            sum = sum - (a(i,j)*x(j))
        end
        x(i) = sum
    end
    iter = 1;
    while (1)
    sentinel = 1;
    for i = 1:n
        old = x(i)
        sum = b(i)
        for j = 1:n
            if i~= j
                sum = sum - a(i,j)*x(j)
            end
            x(i) = lambda*sum+(1-lambda)*old
            if sentinel = 1 && x(i) ~= 0
                ea = abs((x(i)-old)/x(i))*100
                if ea > es
                    sentinel = 0;
                end
            end
            iter = iter + 1;
            if sentinel = 1 | iter >= imax
                break
            end
        end
    end

The error I keep receiving is:

>> gaussseidel

Error: File: gaussseidel.m Line: 35 Column: 25

The expression to the left of the equals sign is not a valid target for an assignment.

Why is this?

Answer 1

[David Goodmanson]

Hello Peter, try

if sentinel == 1 && x(i) ~= 0
instead of
if sentinel = 1 && x(i) ~= 0