Re: Multiply a constant to a matrix column
- To: mathgroup at smc.vnet.net
- Subject: [mg16343] Re: [mg16266] Multiply a constant to a matrix column
- From: Robert Pratt <rpratt at math.unc.edu>
- Date: Sun, 7 Mar 1999 01:05:57 -0500
- Sender: owner-wri-mathgroup at wolfram.com
Just use ordinary matrix multiplication. First define
B={{1,0,0},{0,100,0},{0,0,1}}
Then do
A.B
Rob Pratt
Department of Mathematics
The University of North Carolina at Chapel Hill
CB# 3250, 331 Phillips Hall
Chapel Hill, NC 27599-3250
rpratt at math.unc.edu
http://www.math.unc.edu/Grads/rpratt/
On Fri, 5 Mar 1999, Hyo ahn wrote:
> 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?
>
> Thanks.
>
> Hyo Ahn
> KAERI