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Re: Think before write (Ax=B)


From: Johan Kullstam
Subject: Re: Think before write (Ax=B)
Date: 31 Jul 2000 21:55:36 -0400
User-agent: Gnus/5.0807 (Gnus v5.8.7) Emacs/20.7

Alfredo Tomasini <address@hidden> writes:

> Sorry for the studip question, resonably Muzaffer said
> 
> >Isn't it obvious that x = B * inv(A) ? The inverse should do the right
> >thing.
> 
> ( actually x= inv(A)*B)
> 
> I have to check if my brain is connected sometime ...

inv(A)*B has two flaws

1) numerical problems with accuracy
2) slowness

unless you need inv(A) in and of itself, don't bother.

for one-shot use AŠÜB.  if you have multiple B's, either arrange them
all in a big matrix B = [B1,B2,B3,...,Bn] or try the LU
decomposition (and use ŠÜ for applying the result of that).

-- 
J o h a n  K u l l s t a m
address@hidden
Don't Fear the Penguin!



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