Since your description of the problem is a simple one-liner and lacks additional details, I will show the design of the simplest possible two-input fuzzy controller, using one's preferred design of 'All-Encompassing' membership functions (as long as the membership value is above the absolute 0) and a single rule. This approach is inspired by Professor László T. Kóczy, a prominent figure in the field of fuzzy systems.
%% Simplest two-input fuzzy controller
fis = sugfis;
% Fuzzy Input E
fis = addInput(fis, [-1 +1], 'Name', 'E');
fis = addMF(fis, 'E', 'gaussmf', [0.5 0], 'Name', 'All-Encompassing');
% Fuzzy Input CE
fis = addInput(fis, [-1 +1], 'Name', 'CE');
fis = addMF(fis, 'CE', 'gauss2mf', [0.25 -0.5 0.25 0.5], 'Name', 'All-Encompassing');
% Fuzzy Output
fis = addOutput(fis, [-2 +2], 'Name', 'U');
Kp = 1; % proportional gain
Kd = 1; % derivative gain
fis = addMF(fis, 'U', 'linear', [Kp, Kd, 0], 'Name', 'Linear_Plane');
% Fuzzy Rule
fis = addRule(fis, "If E is All-Encompassing and CE is All-Encompassing then U is Linear_Plane");
%% dynamical system
function dx = ode(t, x, fis)
dx = zeros(2, 1);
error = 1 - x(1);
ce = 0 - x(2);
Fctrl = evalfis(fis, [error, ce]);
dx(1) = x(2);
dx(2) = Fctrl;
end
%% plot results
[t, x] = ode45(@(t, x) ode(t, x, fis), [0 20], [0; 0]);
figure
plot(t, x), grid on
xlabel('t'), ylabel('\bf{x}(t)'), title('Step Response')
legend('x_1', 'x_2', 'location', 'east')
figure
subplot(211)
plotmf(fis, 'input', 1), grid on, ylim([-0.2, 1.2]), xlabel('Error'), title('Only one membership function of E')
subplot(212)
plotmf(fis, 'input', 2), grid on, ylim([-0.2, 1.2]), xlabel('Change in Error'), title('Only one membership function of CE')
figure
opt = gensurfOptions('NumGridPoints', 51);
gensurf(fis, opt);
xlabel('Error'), ylabel('Change in Error'), zlabel('U')
title ('Fuzzy Control Surface')
figure
plotrule(fis, Inputs=[0.25, 0.75])
