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 ?