Re: Multiply a constant to a matrix column
- To: mathgroup at smc.vnet.net
- Subject: [mg16339] Re: Multiply a constant to a matrix column
- From: phbrf at t-online.de (Peter Breitfeld)
- Date: Sun, 7 Mar 1999 01:05:54 -0500
- Organization: das ist ein breites Feld ...
- References: <7bo0gg$dop@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Hyo ahn <heahn at nanum.kaeri.re.kr> schrieb:
> Hi,
>
> I would like to multiply a constant number to a certain column of an existing
> matrix in Mathematica and I am having a hard time.
>
> First, I have a 1000 x 3 matrix A. There is no command that allow me to
> multiply a constant number to a specific column (let say I want to multiply
> 100 to the second column), so I extract three columns
> separately using
>
> A1 = A[Range[1,1000],Range[1,1]];
> A2 = A[Range[1,1000],Range[2,2]];
> A3 = A[Range[1,1000],Range[3,3]];
>
> Then I multiply a constant to a extracted
> column which is a vector now. So I did
>
> A2b = 100 A2;
>
> Then I recombined the columns as
>
> A4 = ColumnJoin[A1,A2b,A3]
>
> but I found out that ColumnJoin command does not worked the way I expected
> it to be.
>
> Could anyone know a simple solution to this problem?
I don't know how fast and memory consuming this will be for big
matrices, but you can try:
At=Transpose[A]; At[[2]]=100*At[[2]]; A=Transpose[At]
es gruesst
Peter
--
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Peter Breitfeld, Saulgau, Germany (PGP public key: 08548045)