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

*To*: mathgroup at smc.vnet.net*Subject*: [mg54475] Re: [mg54431] Re: Why does Inverse[M] hesitate?*From*: DrBob <drbob at bigfoot.com>*Date*: Mon, 21 Feb 2005 03:44:43 -0500 (EST)*References*: <200502200509.AAA20149@smc.vnet.net>*Reply-to*: drbob at bigfoot.com*Sender*: owner-wri-mathgroup at wolfram.com

>> This is becuase you used MatrixForm which puts a wrapper around the expression. Actually, it's because MatrixForm DOESN'T act as a wrapper. According to Help, it doesn't interfere with evaluation, but clearly, it does. Bobby On Sun, 20 Feb 2005 00:09:53 -0500 (EST), Bill Rowe <readnewsciv at earthlink.net> wrote: > 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 > -- > To reply via email subtract one hundred and four > > > > -- DrBob at bigfoot.com www.eclecticdreams.net

**References**:**Re: Why does Inverse[M] hesitate?***From:*Bill Rowe <readnewsciv@earthlink.net>