I believe you want to visualise the various amplitudes of sin wave in continous segments, that is the first signal should be in time intervall (0-1) with 1 magnitude and the next signal from (1-2) with the increased magnitude and so on.
As mentioned by @Jan, you can use the axes command to add to the same plot and you can also follow the given method to visualize in a better manner
f = 1;
a = 0.1;
Fs = 1000;
t1 = 1;
figure;
axes('NextPlot', 'add');
while 1 % Runs until you press Ctrl-c
%since we want to visualise the new amplitude in the segment-[t1-1,t1]%
t_array = t1-1 : 1/Fs :t1-1/Fs;
x = a * sin(2 * pi * f * t_array);
plot(t_array, x);
%add pause to visualise the graph as amplitude grows%
pause(1);
t1 = t1 + 1;
a=a+0.1;
end
Hope this helps and satisfies your requirements.
