Re: Why does Inverse[M] hesitate?
- To: mathgroup at smc.vnet.net
- Subject: [mg54431] Re: Why does Inverse[M] hesitate?
- From: Bill Rowe <readnewsciv at earthlink.net>
- Date: Sun, 20 Feb 2005 00:09:53 -0500 (EST)
- Sender: owner-wri-mathgroup at wolfram.com
On 2/19/05 at 2:32 AM, skirmantas.janusonis at yale.edu (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.
Right. This is becuase you used MatrixForm which puts a wrapper around the expression.
If you do
A={{(1-g)-1,1},{-w P(1-g)/C,-1}}//MatrixForm
MatrixQ[A]
you will get False indicating A is not a matrix. The same is true of B. Consequently, neither Inverse nor . can work
There are a couple of ways around this issue. First, you could do
(A={{(1-g)-1,1},{-w P(1-g)/C,-1}})//MatrixForm
(B={{0},{-P(w+1)}})//MatrixForm
This forces assignment to A and B before MatrixForm does its thing. As a consequence,
MatrixQ[A] will evaluate as True and Inverse[A].B will do what you expect.
But I think the more elegant way around this issue is to set the default output display to TraditionalForm and simply not use MatrixForm
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