Re: [Blitz-support] Can you determine tensor indices at runtime?

[Tama Ma <pin...@it...>]

Hi, 

      If what you want is matrix product, then the following is the solution:


typedef double valuetype;

blitz::Array<valuetype, 2> A;
blitz::Array<valuetype, 1> B;
blitz::Array<valuetype, 1> C;

A.resize(2,2);
B.resize(2);
C.resize(2);

C = blitz::sum(A(blitz::tensor::i, blitz::tensor::j) * B(blitz::tensor::j)) , blitz::tensor::j);

A.free();
B.free();
C.free();


      Hope this works!


Best regards,
Tama Ma



On Jul 18, 2010, at 10:19 PM, W.P. McNeill wrote:

> I want to do outer multiplication on two Arrays, a 2x2 called A and a 2x1 called B.  If I want to multiply over the first index of A, I can say this:
> 
>   firstIndex i;
>   secondIndex j;
>   C = A(i,j) * B(i);
> 
> If I want to multiply over the second index, I can say this:
> 
>   ...
>   C = A(i,j) * B(j);
> 
> This requires me to decide which index I'm multiplying over when I write the source code.  Is there a way to make a decision about which index to multiply over at runtime?  Is there a way to do this for arbitrary dimensions in a matrix?
> 
> I don't see how to do this from looking at the header files.  I tried calling A(...) and B(...) with TinyVectors of IndexPlaceholder objects, but that doesn't work.
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-- 
ETH Zurich
Tama Ma
Institute for Theoretical Physics
HIT K31.3
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Switzerland

pin...@it...
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