From bug-octave-request at bevo dot che dot wisc dot edu Sun Jan  5 18:52:51 2003
Subject: Re: Operations on matrix referenced by a list of indices
From: Paul Kienzle <pkienzle at users dot sourceforge dot net>
To: =?ISO-8859-2?Q?Igor_=D0ukanovi=E6?= <igor dot mat at uni-mb dot si>
Cc: bug-octave at bevo dot che dot wisc dot edu
Date: Sun, 05 Jan 2003 19:53:14 -0500

Igor Đukanović wrote:  

> However statement
> A([ 1 1])= A([1 1]) + [ 8 9];
> does (same as in Matlab)
> A(1) = A(1) + 9;
> and that's bad.  I want it to do
> A(1) = A(1) + 8; A(1)=A(1) + 9;
> producing
> A(1)=A(1)+8+9;
> otherwise I would not include 1 in index list twice.

I'm guessing your real code is much more complicated which
is why you don't say A(1) += sum(B).

Assuming you have sparse matrices from octave-forge, then instead
of

    A(idx) = A(idx) + B;

you can do something like (untested):

    Bsum = spsum(sparse(1:length(idx),idx,B));
    Bidx = find(Bsum); # perhaps spfind.  spsum ought to return a sparse 
vector.
    A(Bidx) += Bsum(Bidx);

> P.S.  Info:  octave-2.1.36
> Windows 98 on Pentium

Use the older version of octave-forge unless you want to install a newer 
version of
octave.  2.1.43 requires octave-forge from CVS to compile.

Paul Kienzle
pkienzle at users dot sf dot net




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