Thank you very much for your answer.
Unfortunately, I cannot use any package...
Do you have a solution ?
Thank you in advance


Edouard Hardy


On Tue, Sep 3, 2013 at 11:49 AM, Gerrit Eichner <
Gerrit.Eichner@math.uni-giessen.de> wrote:

> Hello, Edouard,
>
> taking logs of A's elements (so that * turns into +, so to say), using a
> left-multiplication with a certain band matrix of the package Matrix, and
> exponentiating the result again could provide a solution (see below).
>
>
>  I know have the following problem:
>> I have a matrix :
>> A =
>> 1  2  3
>> 4  5  6
>> 7  8  9
>> 9  8  7
>> 4  5  6
>> 3  2  1
>>
>> And I would like to have :
>> B =
>> 1*4*7  2*5*8  3*6*9
>> 4*7*9  5*8*8  6*9*7
>> 7*9*4  8*8*5  9*7*6
>> 9*4*3  8*5*2  7*6*1
>>
>> Here I took the product of 3 rows each time. And 3 needs to be a
>> parameter.
>>
>> Is it possible to do so without any loop ?
>>
>
>
> Caveat: Not very carefully tested!
>
> library( Matrix)
>
> k <- 3
> ones <- lapply( 1:k, function( j) rep( 1, nrow( A) - j + 1)))
> leftmatrix <- bandSparse( n = nrow(A) - k + 1, m = nrow(A),
>                           k = 0:(k-1), diagonals = ones)
>
> exp( leftmatrix %*% log(A))
>
>  Hth  --  Gerrit
>
> ------------------------------**------------------------------**---------
> Dr. Gerrit Eichner                   Mathematical Institute, Room 212
> gerrit.eichner@math.uni-**giessen.de <gerrit.eichner@math.uni-giessen.de>  Justus-Liebig-University Giessen
> Tel: +49-(0)641-99-32104          Arndtstr. 2, 35392 Giessen, Germany
> Fax: +49-(0)641-99-32109        http://www.uni-giessen.de/cms/**eichner<http://www.uni-giessen.de/cms/eichner>
> ------------------------------**------------------------------**---------
>

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