inverse of a matrix with Fraction entries

Robert Kern robert.kern at gmail.com
Wed Nov 24 19:30:44 CET 2010


On 11/24/10 12:07 PM, Daniel Fetchinson wrote:

> The whole story is that I have a matrix A and matrix B both of which
> have rational entries and they both have pretty crazy entries too.
> Their magnitude spans many orders of magnitude, but inverse(A)*B is an
> okay matrix and I can deal with it using floating point numbers. I
> only need this exact fraction business for inverse(A)*B (yes, a
> preconditioner would be useful :))
>
> And I wouldn't want to write the whole matrix into a file, call Maple
> on it, parse the result, etc.
>
> So after all I might just code the inversion via Gauss elimination
> myself in a way that can deal with fractions, shouldn't be that hard.

+1000. This is almost always the right thing to do whether you have floats or 
rationals.

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
  that is made terrible by our own mad attempt to interpret it as though it had
  an underlying truth."
   -- Umberto Eco




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