Lookup values in a 6-D matrix using indices from columns of another matrix.

Trying to look for values in the v_tbl based on index provided by each column of quant_sysplus.

Problem: Runs too slow because I'm using two For loops. Is there a faster way of accessing the values?

v_tbl is a 6-D array that contains values of interest. quant_sysplus is 3-D (1:6,1000,3) array with each column containing a set of indices (1:6) to a value in v_tbl.

The following is what I have so far and it works, but there are a lot of states (121x121x24x7x7x3) that I have to step through. The two For Loops makes it extremely slow when I have 3000 sets of indices to lookup in each state.

for ind_page=1:page %page=3
    for ind_col=1:Np %Np=1000       lookup(1,ind_col,ind_page)=v_tbl(quant_sysplus(1,ind_col,ind_page),quant_sysplus(2,ind_col,ind_page),quant_sysplus(3,ind_col,ind_page),quant_sysplus(4,ind_col,ind_page),quant_sysplus(5,ind_col,ind_page),quant_sysplus(6,ind_col,ind_page)); % Returns the values for each sample
    end
end

I've tried Parfor as well, but was slower probably because the comm overhead was high.

Any suggestions?? Thank you.

David

[Sara]

Have you tried (no loops)

lookup(1,:,:)=v_tbl(quant_sysplus(1,:,:),quant_sysplus(2,:,:),quant_sysplus(3,:,:),quant_sysplus(4,:,:),quant_sysplus(5,:,:),quant_sysplus(6,:,:));

[David Hung]

This was what I thought would work but causes dimension mismatch.

[Sara]

Can you attach your arrays? Just to see what's going on and test different solutions for speed.

[David Hung]

v_tbl and quant_sysplus are attached. quant_sysplus has 30 samples (each row is a sample)(1:12,10,3). Rows 1:6 are the actual indices to be used on v_tbl. Can ignore rows 7:12 for now. v_tbl is populated with some values but most of it is still 0 because I haven't ran through all of the states. For now, Np will have to changed to 10 since there are only 10 columns per page (eventually Np=1000).

Thank you.

Answer 1

[Adam]

sz = size( v_tbl );
lookup = v_tbl( sub2ind( sz, quant_sysplus(1,:,:), quant_sysplus(2,:,:), quant_sysplus(3,:,:), quant_sysplus(4,:,:), quant_sysplus(5,:,:), quant_sysplus(6,:,:) ) );

should work I think.

You need to convert your multi-dimensional subscripts into 1d indices into the 6d array.

[David Hung]

Right on!!!