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rcond: How do I use it?

From: John W. Eaton
Subject: rcond: How do I use it?
Date: Mon, 15 Mar 1999 03:06:57 -0600 (CST)

On 13-Mar-1999, Gary Church <address@hidden> wrote:

| I'm running the most recent stable release of Octave for OS/2. I want to
| use the "rcond" function to estimate the goodness of the inverse of a
| matrix but it doesn't seem to be available to me.
| In one of my programs where I'm calculating the inverse of a large
| Vandermond matrix, I get the following warning:
| warning: inverse: matrix singular to machine precision, rcond =
| 8.67916e-307
| How do I calculate the rcond value directly?

The value of `rcond' in the error message is just an estimate of the
inverse of the condition number of the matrix.  You can use `cond' to
compute the condition number, so 1/cond(x) should give you something
close to rcond(x).


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