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MathGroup Archive 2006

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Bug in RowReduce of a matrix with symbolic entries

  • To: mathgroup at smc.vnet.net
  • Subject: [mg70772] Bug in RowReduce of a matrix with symbolic entries
  • From: "Ruben" <r.tiger74 at gmail.com>
  • Date: Fri, 27 Oct 2006 00:28:08 -0400 (EDT)

Hi all, the Mathematica help browser claims that one can apply
RowReduce to a matrix with numbers and letters, however that's not
true, try to row-reduce the following augmented matrix:

Clear[x, y, z, s, t];
RowReduce[{{
    1, 1, 1, x}, {-2, -1, -1, y}, {-3, -3, -2, z}, {0, 2,
         2, s}, {-2, -4, -5, t}}] // MatrixForm

the output does not contain any expression involving the letters!

Am I doing something wrong?

For the sake of completeness, one can obtain the right answer (the
homogeneous system that makes the above augmented matrix consistent) by
typing:

Clear[a, v, x, y, z, s, t];
a = {{1, 1, 1}, {-2, -1, -1}, {-3, -3, -2}, {0, 2, 2}, {-2, -4, -5}};
answer = NullSpace[Transpose[a]];
v = {x, y, z, s, t};
Thread[answer.v == 0]

(I found this method in this google group).

Thanks for any suggestion you may provide.

Ruben.


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