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MathGroup Archive 2006

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RE: MemberQ

  • To: mathgroup at smc.vnet.net
  • Subject: [mg68554] RE: [mg68503] MemberQ
  • From: "David Park" <djmp at earthlink.net>
  • Date: Wed, 9 Aug 2006 04:20:27 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Bruce,

Because...

set1 = Range[0.0, 1.0, 0.1]
% // InputForm
{0., 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.}
{0., 0.1, 0.2, 0.30000000000000004, 0.4, 0.5,
 0.6000000000000001, 0.7000000000000001, 0.8, 0.9,
 1.}

Try..

set2 = Table[x/10, {x, 0, 10}] // N
% // InputForm
{0., 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.}
{0., 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9,
 1.}

MemberQ[set2, 0.7]
True

But in general you're going to get poor results testing set inclusion with
approximate numbers. You could use something like

Count[set1, x_ /; 0.699 < x < 0.701] > 0
True

David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/


From: Bruce Colletti [mailto:vze269bv at verizon.net]
To: mathgroup at smc.vnet.net


Re Mathematica 5.2.0.0.

Since 0.7 is in the set {0.0, 0.1, 0.2,..., 0.9, 1.0}, why does
MemberQ[Range[0., 1., .1], .7] return False?

Thankx.

Bruce



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