I just had a Matlab experience that made me question everything.
I have two vectors: v1 and v2. Both are of length 10 000 and in double-precision. If I plot them, they look like this:
Clearly, these two vectors are very different - one contains values as high as 30 while the other one contains mostly zeros and maxes out at around 6.8.
So far so good. But now when I plot the difference between the two vectors ( v1-v2) I get this:
And if I calculate the maximum absolute difference between the two:
I get 4.4409e-15! What is going on here!?
Clearly the maximum absolute difference should be around 30, not in the order of e-15 something. So what am I facing here? Is it:
- My Matlab installation that is broken
- My system that is broken and can’t do arithmetic correctly
- My brain that is broken and the result are correct
This is the code I use to replicate the results, and I’m attaching a .mat file with the v1 and v2 vectors:
title('vector #1'), xlim([1 10000])
title('vector #2'), xlim([1 10000])
plot(v1 - v2)
title('vector #1 - vector #2'), xlim([1 10000])
I’m using Matlab 2018a on Windows 10 using a i7-8700K processor.