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Re: no way for simple matrix lookup ?

From: Jonathan C. Webster
Subject: Re: no way for simple matrix lookup ?
Date: Wed, 16 Jun 2004 17:16:41 -0400
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.4) Gecko/20030624 Netscape/7.1

D. Goel wrote:

[1] Suppose A is a nxn matrix.  And b and  c are vectors.  How do i
return elements of A specified by b and c? i.e. Want to return a vector D, such that D(i) = A(b(i), c(i))
Ravel the matrix A out into one long vector, A_vec, using fortran indexing if 
you want.
Then combine vec_b and vec_c into a single index vector into your A_vec.
vec_3 = vec_b + size(A)(1) * (vec_c - 1)

Finally, your new reordered result vector D_vec

D_vec = A_vec(vec_3)

I think thats right, but check it. Think carefully about which should be vec_b 
and vec_c.

Jonathan Webster

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