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Mod and QuotientRemainder are inconsistent

  • To: mathgroup at
  • Subject: [mg124837] Mod and QuotientRemainder are inconsistent
  • From: Szabolcs <szhorvat at>
  • Date: Thu, 9 Feb 2012 05:35:54 -0500 (EST)
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  • Reply-to: comp.soft-sys.math.mathematica at

Mod[12, 0.1] gives 0.1 despite 120*0.1 == 12.  I expect this is because 0.1 is not representable in binary.

QuotientRemainder[12, 0.1] gives {120, 0.} however, which is inconsistent with the result above.

Quotient[12,0.1] gives 120 which is also inconsistent with Mod.

Is this a bug or is it by design?  It seems it is not safe to assume that 

QuotientRemainder[a,b] == {Quotient[a,b], Mod[a,b]}

or that 

Quotient[a,b]*b + Mod[a,b] == a

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