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Re: Mod and QuotientRemainder are inconsistent

  • To: mathgroup at smc.vnet.net
  • Subject: [mg124885] Re: Mod and QuotientRemainder are inconsistent
  • From: Bob Hanlon <hanlonr357 at gmail.com>
  • Date: Fri, 10 Feb 2012 05:58:31 -0500 (EST)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <201202091035.FAA18248@smc.vnet.net>

To get exact results use exact numbers

Mod[12, 1/10]

0

Mod[12, Rationalize[0.1]]

0


Bob Hanlon


On Thu, Feb 9, 2012 at 5:35 AM, Szabolcs <szhorvat at gmail.com> wrote:
>
> 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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