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MathGroup Archive 2005

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Re: Re: Why does Inverse[M] hesitate?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg54472] Re: [mg54390] Re: Why does Inverse[M] hesitate?
  • From: DrBob <drbob at bigfoot.com>
  • Date: Mon, 21 Feb 2005 03:44:40 -0500 (EST)
  • References: <cv6t0c$6re$1@smc.vnet.net> <200502200507.AAA19929@smc.vnet.net>
  • Reply-to: drbob at bigfoot.com
  • Sender: owner-wri-mathgroup at wolfram.com

Yeah, I'd forgotten one of my pet peeves. Read Help for MatrixForm, and it says:

"MatrixForm acts as a â??wrapperâ??, which affects printing, but not evaluation."

But that's just not true.

Bobby

On Sun, 20 Feb 2005 00:07:49 -0500 (EST), David Bailey <dave at Remove_Thisdbailey.co.uk> wrote:

> Skirmantas wrote:
>> The Inverse function sometimes calculates the inverse of a matrix
>> immediately, sometimes it does not. Try this example in Mathematica
>> 5.1:
>>
>> A={{(1-g)-1,1},{-w P(1-g)/C,-1}}//MatrixForm
>> B={{0},{-P(w+1)}}//MatrixForm
>>
>> I get
>> Out: Inverse[(expanded A)].(expanded B)
>>
>> If I do just
>> A={{a,b},{c,d}}
>> B={{e},{f}}
>> Inverse[A].B
>>
>> I get the final correct result.
>>
> If you write A= <some matrix expression> //MatrixForm it displays
> beautifully, but the expression assigned to A actually contains the
> MatrixForm! You can check this by looking at FullForm[A].
>
> You should write A=<some matrix expression>;
> A//MatrixForm
>
> That way the expression containing the MatrixForm gets discarded.
>
> BTW - This example just goes to show how useful it is to include ACTUAL
> CODE with a query!
>
> David Bailey
> dbaileyconsultancy.co.uk
>
>
>
>



-- 
DrBob at bigfoot.com
www.eclecticdreams.net


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