@Jasvin Thank you for your suggestions,
I obtained parabola plane for my task as given below.
y = linspace(0, 1, 100);
x = y - y.^2;
% Plot the data
plot(x*4, y*95, 'linewidth', 2)
% Add axis labels and title
xlabel('Entropy')
ylabel('\alpha')
hold on
title('H - \alpha plane')
xlim([0 1])
ylim([0 90])
set(gca,'FontSize',12);