Re: Problem: a matrix and a box...

• To: mathgroup at smc.vnet.net
• Subject: [mg27269] Re: Problem: a matrix and a box...
• From: "Allan Hayes" <hay at haystack.demon.co.uk>
• Date: Sun, 18 Feb 2001 02:52:06 -0500 (EST)
• References: <96lcto\$gt4@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Bed,

Two suggestions:

M = {{a1,a2,a3,a4},{b1,b2,b3,b4},{c1,c2,c3,c4}}

{{a1,a2,a3,a4},{b1,b2,b3,b4},{c1,c2,c3,c4}};

Drop[M, 1,1]+Drop[M,1,-1]+Drop[M,-1,1]+Drop[M,-1,-1]

{{a1+a2+b1+b2,a2+a3+b2+b3,a3+a4+b3+b4},
{b1+b2+c1+c2,b2+b3+c2+c3,b3+b4+c3+c4}}

ListConvolve[{{1,1},{1,1}}, M]

{{a1+a2+b1+b2,a2+a3+b2+b3,a3+a4+b3+b4},
{b1+b2+c1+c2,b2+b3+c2+c3,b3+b4+c3+c4}}

--
Allan
---------------------
Allan Hayes
Mathematica Training and Consulting
Leicester UK
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565

"Bedrosian Baol" <Bedrosian at MailAndNews.com> wrote in message
news:96lcto\$gt4 at smc.vnet.net...
> Hi
> this is the problem: I have a n x m matrix (with n and m ~3000 elements or
> more)
>
> a1 a2 a3..
> b1 b2 b3..
> c1 c2 c3..
> . . .
> . . .
>
> the algorythm is: compute the summ of the the a1, a2, b1 and b2 elements
(a
> ''gliding box'' 2x2), shifing the ''box'' for 1 column and repeat the sum
of
> the elements (now a2, a3, b2, b3), and so on...
> at the and of the first line, the box return on the second line and
> repeat...
>
> the final resuls would be another matrix like this:
>
> [a1+a2+b1+b2] [a2+a3+b2+b3]...
> [b1+b2+c1+c2] [b2+b3+c2+c3]...
> ...
>
> I'm not very experienced with Math4: there is a simple and easy way for
> reach
> the result?
>
> thanks
> Bed
>
>

```

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