For-loop vectorization to record logical values

Hello, I would like to vectorize the following for-loop.

The idea is to record in the LT matrix links specified in the NEc variable (a logical variable of zeros and ones).

%%Build Link Table
LT = false(nIP,nIP); % [logical] - Link Table (each IP has 4 Neighbors)
% Near Edges
NEIP = NaN(max(sum(NEc)),NE_NoOT); % Near Edge Intersection Points
Nlvi = NaN(NE_NoOT,1); % last valid index for NEIP variable
I=cell(NE_NoOT,1); J=I;
for i = 1:NE_NoOT % Spanning all Near Edge traces
    n = find(NEc(:,i)); % i-th NE trace IP indexes
    Nlvi(i) = size(n,1); % NEIP last valid index for i-th NE curve
    NEIP(1:Nlvi(i),i) = n; % IPs
end
% Far Edges
FEIP = NaN(max(sum(FEc)),FE_NoOT); % Far Edge Intersection Points
Flvi = NaN(FE_NoOT,1); % last valid index for FEIP variable
for i = 1:FE_NoOT % Spanning all Far Edge traces
    n = find(FEc(:,i)); % i-th FE trace IP indexes
    Flvi(i) = size(n,1);
    for j = 1:Flvi(i)-1 % Spanning Fear Edge points on the i-th FE trace
        LT(n(j),n(j+1)) = 1; % record link
        LT(n(j+1),n(j)) = 1; % record same link
    end
    FEIP(1:Flvi(i),i) = n;
end

After the loop I need to keep the LT, NEIP and Nlvi variables.

Any idea?

Thank you

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Answer 1

[Matt J]

I don't anticipate any benefit to getting rid of the outer loop, especially if you really do need all those intermediate variables. However, you can eliminate the inner loop as follows;

    I=cell(NE_NoOT,1); J=I;

    for i = 1:NE_NoOT % Spanning all Near Edge traces

        n = find(NEc(:,i)); % i-th NE trace IP indexes

        I{i}=n(1:end-1).'; J{i}=n(2:end).';

        Nlvi(i) = length(N); % NEIP last valid index for i-th NE curve

        NEIP(1:Nlvi(i),i) = n;

    end

   LT=sparse([I{:}],[J{:}],true,nIP,nIP);
   LT=LT|LT.';

[Alfredo]

Hi Matt J, thank you for your answer.

The truth is that the full code I have to vectorize is the one I've just edited.

I need to store in LT the info collected by the cells I and J, you suggested, in the two main loops.

How can I do it?

Thank you

[Matt J]

The code that creates LT looks exactly the same to me as before.

[Alfredo]

Yes it is, but it adds information to the LT matrix and I can't see how to merge the two sections of my whole code in just one loop. Thank you.

[Matt J]

    I=cell(NE_NoOT,1); J=I;
    for i = 1:NE_NoOT % Spanning all Near Edge traces

       n = find(NEc(:,i)); % i-th NE trace IP indexes
       Nlvi(i) = size(n,1); % NEIP last valid index for i-th NE curve
       NEIP(1:Nlvi(i),i) = n; % IPs

        n = find(FEc(:,i)); % i-th NE trace IP indexes
        I{i}=n(1:end-1).'; J{i}=n(2:end).';
        Flvi(i) = length(n); % NEIP last valid index for i-th NE curve
        FEIP(1:Nlvi(i),i) = n;

    end
   LT=sparse([I{:}],[J{:}],true,nIP,nIP);
   LT=LT|LT.';