an issue with Matrix Index exceed Matrix

I have changed the code to:

      X=data;
      epsilon=1;
      MinPts=37;
      C=0;
      [IDX]=DBSCANf(X,epsilon,MinPts);

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

      function [IDX, isnoise]=DBSCANf(X,epsilon,MinPts)
       C=0;
       n=size(X,1);
      % cluster lables initialize 
  %    IDX=zeros(n,1);   
       D=pdist2(X,X);
       visited=false(n,1);  % produce array of logical false for example, false(2) 
       logical 2x2 zero array 
       isnoise=false(n,1); % array of logical false 

      for i=1:n
          if ~visited(i)
              visited(i)=true;     
              Neighbors=RegionQuery(i,D,epsilon);      
              if numel(Neighbors) < MinPts  % Number of array elements 
                  % X(i,:) is NOISE
                  isnoise(i)=true;
              else
                  C=C+1;
                 IDX= ExpandCluster(i,Neighbors,C,visited,D,epsilon,MinPts,n);
              end

          end
       end

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

        function IDX = ExpandCluster(i,Neighbors,C,visited,D,epsilon,MinPts,n)

        IDX=zeros(n,1);
       IDX(i)=C;
       k = 1;
       while true
       j = Neighbors(k);

       if ~visited(j)

          visited(j)=true;

          Neighbors2=RegionQuery(j,D,epsilon);

          if numel(Neighbors2)>=MinPts

              Neighbors=[Neighbors Neighbors2];   %#ok

           end
        end

        if IDX(j)==0
           IDX(j)=C;
        end
        k = k + 1;
        if k > numel(Neighbors)
          break;
         end
          end
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
      function Neighbors=RegionQuery(i,D,epsilon)
          Neighbors=find(D(i,:)<=epsilon); % distance will work one by one i=1 to 10 
         end

the IDX values are zeros :( ??

Answer 1

[dpb]

Use the debugger to see where your implementation logic breaks down...but, the problem arises from

function IDX =ExpandCluster(i,Neighbors,C,visited,D,epsilon,MinPts)
  IDX(i)=C;
  k = 1;
  while true
    j = Neighbors(k);
    ...
    if IDX(j)==0
      ...

the array IDX will be of size(1,i) and the first time the function is called i==1 but then j isn't directly related to i.

functions have local scope, array IDX inside the function has nothing whatever to to with the array in the calling function; if you intend to be operating on it you'll need to pass it.

Also note that Matlab passes only copy of arrays; any modifications made in the function are again local copies only and array arguments modified not passed back to the calling routine.

Upshot is, allocate IDX in the function if you're building it in the function.

Also your assignment in the calling function will overwrite the previous array definition and IDX will be size as returned from the ExpandCluster function. As you've written logic here the statement

IDX=zeros(n,1);

has no effect at all.

[shawin]

I have changed the code, but iam getting zeros IDX values??

[dpb]

Well, that would appear to be a logic error in that the ExpandCluster function isn't working as you expect.

Use the debugger and work through the logic to see where it isn't doing what you intend...the structure looks ok to return the IDX array; now you've got to work on filling it with what is needed.

[shawin]

@dpb: I do not know where is the error?

[dpb]

Well, we don't either...it's logic error, not syntax and we don't have your data nor even an explanation of what you are trying to do. That's the first part of coding; writing a clear problem statement and defining the data structure so one can implement it in code.

[shawin]

dpb: the algorithm is working well if we have it in the format below : https://pastebin.com/17DgD4EU open link but when separate the method it generates zeros