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MathGroup Archive 2002

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Re: Trouble with inverting matrices

  • To: mathgroup at smc.vnet.net
  • Subject: [mg33758] Re: Trouble with inverting matrices
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Thu, 11 Apr 2002 02:14:15 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

can you post the complete code ? Because otherwise
we can only use our phantasie to find the bug you have
made.

Regards
  Jens

Wyvern wrote:
> 
> Hi,
> When I try to invert a matrix (as it happens, a matrix with the elements
> described in #7 of Nick Trefethen's 10 challenges but of a much smaller
> size) and store that inverse to a variable, I get this error: (for a 2x2
> case)
> Inverse::"sing": "Matrix \!\({\(\({0, 0}\)\), \(\({0, 0}\)\)}\) is
> singular."
> 
> [and then the output of the for loop in which the operation is embedded, and
> then another error:]
> 
> Set::"write": "Tag Times in \!\(inv  \\\\  Null  \\\\  Null  \\\\  Null
> \\\\ \
>  Null  \\\\  Null  \\\\  Null\) is Protected."
> 
> inv is the variable to which I am trying to store the inverse.
> 
> The bizarre part is that if I try to print the the inverses as they are
> generated (my For loop increases the size of the mxm matrix by one each time
> and sets the elements of the matrix and then calculates the inverse) then it
> works fine, as in Print[MatrixForm[Inverse[theMatrix]]]. If I set
> inv = Inverse[theMatrix] it gives the errors above.
> Also, the matrix given in the error for Inverse is NOT the matrix that has
> been passed to Inverse! In the 2x2 case, the matrix is {2,1}{1,3} which is
> invertible. So where is Inverse coming up with this {0,0}{0,0} matrix which
> it (correctly) claims is not invertible? Any help would be much appreciated.
> 
> Marshall Pierce


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