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Re: [Q] Cancel command in 4.1

  • To: mathgroup at smc.vnet.net
  • Subject: [mg27676] Re: [Q] Cancel command in 4.1
  • From: "Ian McInnes" <ian at whisper-wood.demon.co.uk>
  • Date: Sun, 11 Mar 2001 04:04:20 -0500 (EST)
  • References: <98cgj7$fto@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

The problem is due to inexact representation of the constants in the matrix
m.

0.1 is a recurring fraction in binary, and its representation therefore
contains a rounding error. This error prevents the required cancellation,
since multiples of 0.1 are not in general represented as exact multiples of
it.

If instead m is specified as a rational matrix, i.e.
      m = {{3/10, 7/10}, {4/10, 6/10}}
then the result:
      {{1/(-1+lambda)}, {1/(-1+lambda)}}
is achieved.
In fact, Cancel is not required - Mathematica does this automatically.

Regards,

Ian.
"Janusz Kawczak" <jkawczak at math.uncc.edu> wrote in message
news:98cgj7$fto at smc.vnet.net...

>
> Hi
>
> I am having problems with the Cancel command to do the simple task. The
> problem
> can be replicated as follows:
>
> m={{.3,.7},{.4,.6}}
> i=IdentityMatrix[2]
> j={{1},{1}}
> inv=Inverse[lambda i - m]
> Cancel[Factor[inv.j]]
>
> The last command should cancel the common factors, but it does not!
> Any help on that.
> Thank you.
> John.
>






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