mod function return wrong answer?

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Hiroaki Yamamoto 2020-7-4

评论： madhan ravi 2020-7-5

How can I make sure mod(a,b) returns value less than b, without explicitly calling min( mod(a,b), b )?

mod( -eps, 1 ) = 1 when eps ~ 10^-17.

Numerical accuracy is not an issue, but I need mod( a, 1 ) be less than 1.

madhan ravi 2020-7-5

编辑：madhan ravi 2020-7-5

Sindar I suggest moving your comment as an answer

I expected mod( a, m ) < m (less than m),

but numerically mod(a, m) <= m (less than or equal to m) is the result when a = -1e-17 and m = 1.

If, internally, 1 - 10^-17 = 1 is calculated and returned, I think 0 is the mathematically correct return value rather than 1.

madhan ravi 2020-7-5

>> mod( -eps, 1 ) < 1
ans =
    logical
     1

My question is, mathematically which of the following is correct or intended to be implemented.

1) mod(a, m) < m

2) mod(a, m) <= m.

Practically, I found mod(a,m) = m can happen and I do explicit check and avoid problems caused by the case mod(a,m) = m.

madhan ravi 2020-7-5

Practically speaking it depends on what m is.

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