Optimize 3D matrix indexing from vector and 2D matrix

Hi all,

Might be a bit convoluted title, but I can explain best using an example. There must be a way to optimize this, but I can't figure out how. See the example loop below, basically I have the same issue twice. I don't know how to represent the [-1 0 1]+D(k,l) in matrix arithmetic.

K = 25;
L = 3000;
M = 250;

A = zeros(K,L,3);
B  = zeros(K,L);

C = randn(K,L,M);
D = floor(3 + (M-3-1) .* rand(K,L)); % make sure that [-2:2]+D(k,l) is logical index

for k = 1:K
    for l = 1:L
        A(k,l,:) = reshape( C(k, l, [-1 0 1]+D(k,l)), [3 1] );
        B(k,l)   = sum( C(k, l, [-2:2]+D(k,l)) );
    end
end

I'm interessted in an optimized variant of the above snippet. Are there any tricks I can do to get rid of the loop for this specific instance?

[Pim Hacking]

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