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MathGroup Archive 2003

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Testing for invertible matrix

  • To: mathgroup at smc.vnet.net
  • Subject: [mg39676] Testing for invertible matrix
  • From: Bob Harris <NspamITmeLION at MINDnotSPRING.COM>
  • Date: Sat, 1 Mar 2003 02:48:33 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Howdy,

If there some means to test whether a square matrix is invertible, rather
than trying Invert[] and having it fail?

I'm working on a notebook that's searching through randomly generated
matrices, looking for one for which the inverse has certain properties.
Thus inside my search function I have a loop something like this:

    While [... some condition ,
        t = ... create a matrix   ;
        q = Inverse[t] ;

        ... perform some computation using the entries in q
            to determine if the exit condition will be met
        ];

But if t is singular, computing the inverse fails.  Nevertheless my loop
keeps running for a while, but generates a few more annoying messages
(because access to q fails) before it finally quits.

What I would rather do is something like this:

    While [... some condition ,
        t = ... create a matrix   ;
        If [ t is singular, Continue[]];

        q = ... inverse of matrix ;

        ... perform some computation using the entries in q
            to determine if the exit condition will be met
        ];

But looking through the mathematica book, I haven't come across a way to do
that.  I also considered that Inverse[] would have some means for me to tell
it how to handle the failure condition, but I don't see anything in the book
about that.

Thanks in advance for any help,
Bob H
Lawrenceville, GA




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