Would it look like this:
% y = sine(2*pi*f*t)
t1 = linspace(0,10,500);
t2 = linspace(10,50,500);
t3 = linspace(50,60,500);
f1 = linspace(0,100,500);
f2 = repmat(100, [1 numel(t2)]);
f3 = fliplr(f1)
t = [t1 t2 t3];
f = [f1 f2 f3];
figure
subplot(2,1,1)
plot(t,2*pi*f.*t)
title('2*pi*f.*t')
xlabel('t');
ylabel('2*pi*f.*t')
subplot(2,1,2)
plot(t,sin(2*pi*f.*t));
title('sin(2*pi*f.*t)')
xlabel('t');
ylabel('sin(2*pi*f.*t)')
