Why don't 2 signals 180 degrees out of phase add up to an array of zeros?

Question

Shae Morgan 2016-7-27

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/297438-why-don-t-2-signals-180-degrees-out-of-phase-add-up-to-an-array-of-zeros

回答： Walter Roberson 2016-7-27

I have this code:

amp=1;
fs=24000;  
duration=2;
t=0:1/fs:duration;
freq = 1000;
Y=amp*sin(2*pi*freq*t+deg2rad(0));
Yi=amp*sin(2*pi*freq*t+deg2rad(180));
combined=Y+Yi;
plot(t(1:24),Y(1:24),'b'); hold on;
plot(t(1:24),Yi(1:24),'r'); hold on;
plot(t(1:24),combined(1:24),'g')
combined(1:24)

My question is: Why doesn't 'combined' add the two out of phase signals to an array of zeros? shouldn't 2 signals 180 degrees out of phase cancel each other out completely? Why are there still very small fluctuations about zero? Is it something about the "deg2rad" function, but they just say "meh, the difference from zero is close enough"?