Критерий Найквиста - неопределенная переменная в алгоритме

Пишу алгоритм, проверяющий устойчивость замкнутой системы по критерию Найквиста (http://en.wikipedia.org/wiki/Nyquist_stability_criterion)

    function answear=stability(re,im)
%% Function check stability of system
%re is real part of transmitation
%im is imagine part of transmitation

%% Check number of vectors elements
re(end +1:5) = 0;
im(end +1:5) = 0;

if( length(re) > length(im))
    root = length(re);
else
    root = length(im);
end

for w=1:root
    tran(w) = re(1) + re(2)*w.^1 + re(3)*w.^2 + re(4)*w.^3 + re(5)*w.^4 +1i*(...
     im(1) + im(2)*w.^1 + im(3)*w.^2 + im(4)*w.^3 +im(5)*w.^4);
end

%% Algorithm
switch root
    case 0
        exist('Write nonzero numbers', 'var')
    case 1
    for w=1:length(w)
        if( real(tran(w)) > 0 && imag(tran(w)) > 0) 
            answear=1;
        else
            answear=0;
        end
    end
    case 2
    for w=1:length(w)
        if( real(tran(w)) > 0 && imag(tran(w)) > 0) 
            if( real(tran(w)) < 0 && imag(tran(w)) > 0) 
                answear=1;
            else
                answear=0;
            end
        end
        end
    case 3
    for w=1:length(w)
        if( real(tran(w)) > 0 && imag(tran(w)) > 0) 
            if( real(tran(w)) < 0 && imag(tran(w)) > 0) 
                if( real(tran(w)) < 0 && imag(tran(w)) < 0) 
                    answear=1;
                else
                    answear=0;
                end
            end
        end
    end
    case 4
    for w=1:length(w)
         if( real(tran(w)) > 0 && imag(tran(w)) > 0) 
            if( real(tran(w)) < 0 && imag(tran(w)) > 0) 
                if( real(tran(w)) < 0 && imag(tran(w)) < 0)
                    if( real(tran(w)) > 0 && imag(tran(w)) < 0) 
                        answear=1;
                    else
                        answear=0;
                    end
                end
            end
         end
    end
end

%% Answear
if answear==1
    disp('System unstable')
else
    disp('System stable')
end
plot(real(tran),imag(tran)) 
grid on

end

Функция возвращает

Неопределенная функция или переменная.

Ошибка в стабильности (строка 87), если ответ==1

Значит алгоритм плохо написан?