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MathGroup Archive 2000

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Pb with ZeroTest

  • To: mathgroup at smc.vnet.net
  • Subject: [mg23723] Pb with ZeroTest
  • From: jmcornil <jmcornil at club-internet.fr>
  • Date: Mon, 5 Jun 2000 01:09:16 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Hello,

I am trying to use the option ZeroTest in the function Inverse
but I desperatly get a crash of the Kernel.
Can someone tell me what is wrong in the following lines ?


First a singular matrix

     In[3]:=
       m = Table[Sin[i + j - 1], {i, 3}, {j, 3}]
       Simplify[Det[m]]
     Out[3]=
       {{Sin[1], Sin[2], Sin[3]}, {Sin[2], Sin[3], Sin[4]},
     {Sin[3], Sin[4],
     Sin[5]}}
     Out[4]=
       0

Then a non singular but "nearly singular"


     In[5]:=
       mn = 0.001  Round[1000*(m // N)]
       Inverse[mn]
     Out[5]=
       {{0.841, 0.909, 0.141}, {0.909, 0.141, -0.757},
        {0.141, -0.757, -0.959}}
     Out[6]=
       {{7012.83, -7574.5, 7010.12}, {-7574.5, 8182.5, -7572.64},
        {7010.12, -7572.64,  7007.21}}

so far so good : the inverse uses large number
since the initial matrix is singular !

But if I try to use the option ZeroTest, I crash the kernel :


     In[7]:=
       Inverse[mn, ZeroTest -> Function[x, Abs[x] <= 0.001]]

        <<<<< C R A S H >>>>>>

What am I doing wrong ?

Thanks in advance


Jack-Michel CORNIL



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