A sine wave type of curve is the expected output of plot(A) in this case. If you are not sure why this is the case, please refer to the documentation about the plot function: plot documentation
In order to plot the PWM you will have to create this signal based on each entry of your table A. First entry 128 means 128/255 = 50.2% duty cycle.
With Arduino's PWM frequency at about 500Hz, one cycle would be 2 miliseconds. Therefore the PWMsignal should start with ones for 50.2% of 2 ms then zeros for the rest of the cycle.
One possibility based on the A table that you gave would be something along those lines. Feel free to adapt it to your needs.
dutyCycle = A/255;
PWMsignal = [];
for entry = 1:numel(A)
temp = zeros(1,100);
temp(1:floor(100*dutyCycle(entry)))=1;
PWMsignal = [PWMsignal, temp];
end
time = 0:2/100:numel(A)*2-2/100; % each cycle length is 2 ms
plot(time,PWMsignal)
xlabel('time (ms)')
ylabel('PWN amplitude')
