Re: 2 Simple Mathematica Questions. (regarding tensors and matrices)
- To: mathgroup at smc.vnet.net
- Subject: [mg45103] Re: 2 Simple Mathematica Questions. (regarding tensors and matrices)
- From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
- Date: Wed, 17 Dec 2003 07:54:22 -0500 (EST)
- Organization: Universitaet Leipzig
- References: <brmqjh$oc2$1@smc.vnet.net>
- Reply-to: kuska at informatik.uni-leipzig.de
- Sender: owner-wri-mathgroup at wolfram.com
Hi,
you know to use Part to access H[[1,3,21]] but you don't know
to access the elements of L1 with L1[[i,j]] and L2[[k,l]]
*and* you don't like
Outer[Times, L1, L2, 2]
that need no explicit element access at all
Since the full matrix A is different for the function call
to the Function A[i,j] you *must* use a different symbol
to denote a matrix *element*.
What is with
A=Array[a[i,j],{i,3},{j,3}]
??
Regards
Jens
"Ashok. R" wrote:
>
> Greetings.
>
> This is my first question:
>
> I am trying to form a 4-tensor, H, whose (i,j,k,l) components are given by
> H(i,j,k,l) = M(i,j)A(k,l) where M and A are 2-Tensors (Matrices). This is
> what I have been doing so far:
> L1 = Array[M, {3, 3}]
>
> L2 = Array[A,{3,3}]
>
> H = Table[L1[i,j]*L2[k,l] {i,3},{j,3},{k,3},{l,3}]
>
> The last statement gives a long output, but not the the correct result. I
> want to be able to say
>
> H[[1,3,2,1]] and get M[1,3]A[2,1] as output.
>
> Can someone familiar with tensor manipulation in Mathematica tell me how to
> do this ?
>
> ----------------------------------------------------------------------------
> ---------------------
>
> This is my second question:
>
> I want to assign a matrix, A, that has three rows and three columns and each
> element is identified by A[i,j]
>
> L1 = Array[A,{3,3}] works, but the array is called L and not A. I tried
>
> A = Array[A,{3,3}] and that, as expected, gave me a warning about
> recursions.
>
> Thank you for your assistance. I wish you a pleasant day.
>
> Ashok