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MathGroup Archive 2004

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Re: Transpose matrix does not work when MatrixForm is used, why?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg45411] Re: Transpose matrix does not work when MatrixForm is used, why?
  • From: Dr Bob <drbob at bigfoot.com>
  • Date: Tue, 6 Jan 2004 04:17:29 -0500 (EST)
  • References: <001901c3d3c0$c95cf580$6401a8c0@bcolletti>
  • Reply-to: drbob at bigfoot.com
  • Sender: owner-wri-mathgroup at wolfram.com

This is related to an ongoing thread on computing Transpose (and other 
functions) of MatrixForm objects. There should be a better answer, but 
here's one in the meantime:

data = Array[{# + Random[], # - Random[]} &, {100}];
z = Regress[data, {1, x, x^2}, x, RegressionReport -> CovarianceMatrix]
X = CovarianceMatrix /. (z /. MatrixForm -> Identity)
X[[2, 2]]

This also works, but NOT when Ted Ersek's suggested fix for MatrixForm is 
installed:

X = CovarianceMatrix /. z /. MatrixForm -> Identity

Bobby

"Bruce W. Colletti" <bcolletti at compuserve.com> wrote in message 
news:<btb8oi$jp4$1 at smc.vnet.net>...
> Re Mathematica 5.0 running under WinXP Home.
>
> Am using...
>
>     z = Regress[...RegressionReport->CovarianceMatrix];
>     X = CovarianceMatrix /. z;
>
> ...to extract the given matrix. However, when I use X[[k,k]] to access 
> the k'th diagonal element, I get a row instead!  The culprit is that 
> MatrixForm is the X-head (as FullForm reveals).
>
> How can I strip away this head and make X a list of lists?
>
> Thankx.
>
> Bruce




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