Does sin() have an error?

2012 10 24
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From the command line: >> 6*pi
ans =
18.8496
>> sin(ans)
ans =
-7.3479e-16
Really? Is that a rounding error? Is there a way to get the correct value?

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Matt Fig
Matt Fig 2012-10-24
编辑：Matt Fig 2012-10-24

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That is the correct value for floating point arithmetic.
sin(pi) % Same as your example.
If you want to get the exact value, use the symbolic toolbox.
double(vpa('sin(pi)'))

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Patrick Kelley
Patrick Kelley 2012-10-24
Yeah, I said rounding error when I meant precision error. Good old floating point binary format... I haven't used the symbolic toolbox much but I'll give it another look. Thanks for the quick answer.

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