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MathGroup Archive 1997

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Sums vs Map efficiency

  • To: mathgroup at smc.vnet.net
  • Subject: [mg7715] Sums vs Map efficiency
  • From: Christophe Pichon <pichon at astro.unibas.ch>
  • Date: Wed, 2 Jul 1997 14:21:36 -0400 (EDT)
  • Organization: University of Basel, Switzerland
  • Sender: owner-wri-mathgroup at wolfram.com

Hello !



Does anyone know how to code the following 
in a tensor (more efficient than sums) form ?

here A1 is a (n,n,n)tensor and (A1,A2,a) are  n*n matrices 

gm=Table[
 Sum[ A1[[i,j,k]]*
 A2[[i1,k1]]*
a[[i,i1]]* a[[j,j1]]
,{i1,n},{j1,n},{i,n},{j,n}]
,{k,n},{k1,n}]//Flatten;


For some reason in that form it seems to take quite a long time to 
process gm. (here a is symbolic a= {{a11,a12...} ... ann}} ) 


What I am after is an expression involving Map and Thread and
Transpose  ... ?
but I tried for a while with little success so far.



Cheers


Christophe


  E-mail: pichon at astro.unibas.ch


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