function ia = roehrenfkt(k, ug)

ia = zeros(4,21);
i = 1;

% Vier Kennlinien
for ua = 100:50:250

    % Steuerspannung
    ust = ug + (ua + k(3))/k(1);
    
    % Anodenstrom
    for j = 1:length(ug)
        if ust(j) <= 0
            ia(i,j) = 0;
        else
            ia(i,j) = k(2) * ust(j)^(3/2);
        end
    end
    i = i + 1;
end

% Matrix als Vektor umschreiben
ia = reshape(ia,1,84);
end