• To: mathgroup at smc.vnet.net
• Subject: [mg26478] RE: [mg26472] simple questions about matrices
• From: "David Park" <djmp at earthlink.net>
• Date: Thu, 28 Dec 2000 02:52:18 -0500 (EST)
• Sender: owner-wri-mathgroup at wolfram.com

```Cristian,

mat = Table[Random[Integer, {1, 9}], {i, 3}, {j, 4}]
{{5, 8, 2, 3}, {5, 1, 1, 4}, {8, 5, 5, 8}}

To add the entries in each row, in Version 4 use the shorthand for Apply at
Level 1

Plus @@@ mat
{18, 11, 26}

In Version 3

Plus @@ # & /@ mat
{18, 11, 26}

To add the entries in each column...

columnsum = Plus @@@ Transpose[mat]
{18, 14, 8, 15}

To add a new row with the sum of the columns...

Join[mat, {columnsum}]
{{5, 8, 2, 3}, {5, 1, 1, 4}, {8, 5, 5, 8}, {18, 14, 8, 15}}

Transpose[Join[Transpose[mat], {{1, 1, 1}}]]
{{5, 8, 2, 3, 1}, {5, 1, 1, 4, 1}, {8, 5, 5, 8, 1}}

Also, look at the routines in the following package...

Needs["LinearAlgebra`MatrixManipulation`"]

To add a column we append to each row...

AppendRows[mat, Transpose[{{1, 2, 3}}]]
{{5, 8, 2, 3, 1}, {5, 1, 1, 4, 2}, {8, 5, 5, 8, 3}}

To add a row we append to each column...

AppendColumns[mat, {Plus @@@ Transpose[mat]}]
{{5, 8, 2, 3}, {5, 1, 1, 4}, {8, 5, 5, 8}, {18, 14, 8, 15}}

David Park

> From: Cristian Opazo-Castillo [mailto:cropazo at vassar.edu]
To: mathgroup at smc.vnet.net
>
> Hello all:
>
> I hope that someone is still working and could help me with this...
>
> (a) I have a (m,n) matrix a with integer entries. How can I construct
> a separate list with the totals of adding the entries of either the
> rows or columns?
>
> (b) How can I construct a (m+1,n) matrix where the new row's entries
> are the sums of all numbers on each column?
>
> (c) In general, how can I attach additional columns (o rows) to an
> existing matrix?
>
> Thanks a lot and Happy Holidays,
>
> Cristian
>
>
>

```

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