MATLAB: (a + b) + c ≠ a + (b + c)

addadditionassociativefloating pointfloating point error.sum

I'm new to Matlab
Is there any way to find a, b and c so that (a + b) + c ≠ a + (b + c) I know addition is not associative in floating point, but is there any way to do that in Matlab?

Best Answer

Hi peluca6,
try 0.1 0.2 0.3
These situations are not hard to find. If you just take three random floating point numbers between 0 and 1,
a = rand
b = rand
c = rand
(to make a vector or matrix of random numbers, see 'help rand') and take a look at the quantity
((a+b)+c) - (a+(b+c))
it is nonzero about 17% if the time.
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