Re: Switch rows!

• To: mathgroup at smc.vnet.net
• Subject: [mg32378] Re: Switch rows!
• From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
• Date: Thu, 17 Jan 2002 02:23:31 -0500 (EST)
• Organization: Universitaet Leipzig
• References: <a23fhk\$9le\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Hi,

a) pivoting work with a pivot array, that avoid the
explicit copy/exchange operation of rows ...
the rows are accessed as matrix[[pivot[[i]]]] instead of
matrix[[i]] and "exchanging" a row is an exchange
of the two integers in pivot and not an exchange of
the m numbers in a row.

b) You have to use the HoldFirst attribute:

SetAttributes[RowSwap,HoldFirst]

RowSwap[ matrix_, row1_Integer, row2_Integer ] :=
Block[{tmp = matrix[[row1]]},
matrix[[row1]]=matrix[[row2]];
matrix[[row2]]=tmp;
]

Regards
Jens

> _____________
Rebeka Renko wrote:
>
> Hi!
>
> I have another question. While I was writting a
> program for partial pivoting, I used a program bellow
> for switching rows in a matrix. It works fine, when I
> use it separetly, but if I include it into a programm,
> it returns an error. I believe this is because of the
> BLOCK command, or am I wrong? How can it be changed,
> so that it would fit my programm?
>
> Regards,
> Rebeka
>
> Programm:
> RowSwop[ matrix_, row1_, row2_ ] :=
> Block[{temp = matrix}, temp[[row1]] = matrix[[row2]];
>     temp[[row2]] = matrix[[row1]]; temp ]
>
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```

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