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MathGroup Archive 2005

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Re: Matrices with Mathematica 5.1

  • To: mathgroup at smc.vnet.net
  • Subject: [mg63331] Re: Matrices with Mathematica 5.1
  • From: Bill Rowe <browe51 at earthlink.net>
  • Date: Sat, 24 Dec 2005 07:18:56 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

On 12/23/05 at 5:08 AM, drizkol at gmail.com (drizkol) wrote:

>I would like to solve the system given by:

>[1  7  -2  0  -8  -3]
>[0  0  1  1    6   5]
>[0  0  0  1    3   9]
>[0  0  0  0    0   0]

>Where the matrix is a typical matrix in the form x1+x2+...+xn = b
>where b is the last item in the row.  For example, row 1 could be
>written as x1 + 7x2 - 2x3 -8x4 = -3.  How could I get mathematica
>to solve this matrix?  I understand how to build a matrix, I just
>need to know the operation to run on it.  I tried to use
>LinearSolve but I did something wrong.  Is there a built-in
>operation to solve these matrices?  If so, please tell.  Thanks.

LinearSolve is the built in function used to solve such a problem. The reason LinearSolve won't work in this case is because your matrix represents an undetermined system. That is taking each column (except the last) to be a variable, you have 5 unknowns and 3 conditions. The last row does nothing for you since it represents the trivial identity 0==0.


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