[petsc-dev] Solving under determined systems

Matthew Knepley knepley at gmail.com
Wed Sep 21 21:07:19 CDT 2016

On Wed, Sep 21, 2016 at 8:24 PM, Mark Adams <mfadams at lbl.gov> wrote:

> I thought least squares was for tall skinny (overdetermined) solves? I
> have a short fat (5 x ~100) matrix to solve.

Stefano is right. It will give you the minimum norm solution, which is the
x consistent with the equations and with the minimum norm.


> On Wed, Sep 21, 2016 at 4:24 PM, Stefano Zampini <
> stefano.zampini at gmail.com> wrote:
>> Mark,
>> You can use KSPLSQR
>> Stefano
>> Il 21 set 2016 11:21 PM, "Mark Adams" <mfadams at lbl.gov> ha scritto:
>>> I want to solve for w in V' w = b, where V is tall and skinny. So a
>>> short fat matrix "solve". This is underdetermined. I would like to minimize
>>> the two norm (or any norm) of w. This looks like an optimization problem,
>>> would TAO do this?
>>> Mark

What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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