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Re: Question on Mod[]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg35991] Re: [mg35970] Question on Mod[]
  • From: Andrzej Kozlowski <andrzej at tuins.ac.jp>
  • Date: Sun, 11 Aug 2002 05:13:52 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

I think the Help Browser is only "approximately correct on this point". 
Although it says:

Mod[m, n] is equivalent to m - n Quotient[m, n]

this is only really always true for exact numbers. Thus in your case:

In[21]:=
Mod[Rationalize[3.5],Rationalize[0.1]]

Out[21]=
0

and same for

In[22]:=
Rationalize[3.5]-Rationalize[0.1 
]Quotient[Rationalize[3.5],Rationalize[0.1]]

Out[22]=
0

For inexact numbers this relationship holds "almost everywhere". I 
suspect this is due to the fact that arithmetic in Mathematica is in 
fact binary.

Andrzej Kozlowski
Toyama International University
JAPAN
http://platon.c.u-tokyo.ac.jp/andrzej/


On Saturday, August 10, 2002, at 05:05  AM, Souvik Banerjee wrote:

> Hello Group,
>
> Why does Mod[3.5,0.1] gives 0.1?
>
> However,
> 3.5 - 0.1 Quotient[3.5,0.1] gives 0
>
> Thanks,
>
> -Souvik
>
>
>
>
>
>



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