Re: [Boost-users] proto for array expressions

Subject: Re: [Boost-users] proto for array expressions
From: Eric Niebler (eric_at_[hidden])
Date: 2008-12-18 19:45:35

James Sutherland wrote:
> 
> On Dec 18, 2008, at 3:46 PM, Eric Niebler wrote:
> 
>> Daniel Oberhoff wrote:
>>> Now with proto I was wondering how hard it would be to build an et 
>>> engine for array math. Basically I am interested in general tensor 
>>> notation, and the resulting expressions should be iteratable 
>>> efficiently. think (advanced example):
>>> a_ij = b_i * (c_j - sum(d_ijk, k = [i-1,1])
>>
>> I don't understand your notation. What are a_ij et. al.?
>>
> Presumably Einstein notation:
>   a_i  = vector
>   a_ij  = 2D matrix
>   a_ijk = 3D array
> so that
>   b_i c_j
> is the outer product of two vectors, producing a matrix...

I guess I'm dense, but I still don't get it. What does this expression mean?

   a_ij = b_i * (c_j - sum(d_ijk, k = [i-1,1])

At any rate, it requires a domain expert to say how hard it would be to 
implement a given DSEL, and I'm not a linear algebra domain expert. I've 
done my best to document Proto extensively, and I can answer questions 
about Proto but not about linear algebra.

-- 
Eric Niebler
BoostPro Computing
http://www.boostpro.com