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From: Mats Weber <Mats.Weber@elca-matrix.ch>
Subject: Re: Ada implementation of QR decomposition
Date: 1997/07/25
Message-ID: <33D88188.F6871789@elca-matrix.ch>#1/1
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References: <33D7607A.52BFA1D7@digicomp.com>
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Organization: ELCA Matrix SA
Reply-To: Mats.Weber@elca-matrix.ch
Newsgroups: comp.lang.ada,sci.math.num-analysis
Date: 1997-07-25T00:00:00+00:00
List-Id: <comp.lang.ada>


I don't know what a QR decomposition is, but I have a generic component that
does this:

    -- Decomposes A in a product of two matrices L and U such that L*U = A,
    -- where L is a lower triangular matrix with all diagonal
    -- coefficients equal to ONE and U is an upper triangular matrix.
    -- (L and U are stored in A with zero coefficients omitted)
    -- P is the permutation of the rows of A necessary to achieve the
    -- decomposition in the case of zero pivots, P_ODD is set to TRUE if P
    -- is an odd permutation and PERMUTED is set to FALSE if P is the
    -- identity permutation.

It is not 100% suitable for numerical work (I used it for operations in finite
fields) because it doesn't choose the pivot very effectively (it just makes
sure it is non-zero), but that should be easy to change. Just tell me if it
suits your needs and I'll post it.