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MathGroup Archive 2001

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numerics

  • To: mathgroup at smc.vnet.net
  • Subject: [mg27276] numerics
  • From: Matt.Johnson at autolivasp.com
  • Date: Fri, 16 Feb 2001 03:58:25 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

mathematica gurus--

Here's a frustrating problem, which seems to be simple.  I can calculate a
matrix by hand and enter it into Solve or Reduce and get the correct
relationships:

In[108]:=
mat = Partition[{-0.2, 0.1, 0, 0.1, -0.3, 0.1, 0.1, 0.2, -0.1}, 3];
Reduce[mat.{x1, x2, x3} == {0, 0, 0}, {x1, x2, x3}]
Out[109]=
x1 == 0.5 x2 && x3 == 2.5 x2

However, if I try to manipulate the matrix in Mathematica then solve, it doesn't work:

In[110]:=
mat1 = Partition[{0.8, 0.1, 0.1, 0.1, 0.7, 0.2, 0, 0.1, 0.9}, 3];
imat = IdentityMatrix[Length[mat1]];
newmat = Transpose[mat1] - imat;
In[113]:=
newmat == mat
Out[113]=
True
In[114]:=
newmat === mat
Out[114]=
False
In[115]:=
Reduce[newmat.{x1, x2, x3} == {0, 0, 0}, {x1, x2, x3}]
Out[115]=
x1 == 0. && x2 == 0. && x3 == 0.

any input?

-matt
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