MATLAB: ” Attempted to access sorted_evalue(1); index out of bounds because numel(sorted_evalue)=0. ” how to remove this??

MATLAB

 %calculate eigen vector & eigen value of cm = evector & evalue
    evector = dfdb * rvector;
    evalue = diag( rvalue );
    %clear rvector rvalue
    disp( 'Calculated Eigen Vectors & Eigen Values of CM' );
    [sorted_evalue, index] = sort( evalue );            %sorted in acending order
    sorted_evalue = flipud( sorted_evalue );            %rearranged in decending order
    index = flipud( index );                            %rearranged corresponding indies also
    %Now rearrange eigenvectors in the order of rearranged eigen values
    evector( :, 1:nof ) = evector ( :, index );
    smallest_evalue = (1/100) * sorted_evalue(0);            % to obtain the effective eigen values
    for i = 1:nof
        if (sorted_evalue(i) < smallest_evalue )
            break;
        end
        evalue = [ ];
    end
    index = i+1;

Best Answer

%calculate eigen vector & eigen value of cm = evector & evalue
    if isempty(dfdb) || isempty(rvector)
      error('Need a non-empty dfdb and rvector');
    end
    evector = dfdb * rvector;
    evalue = diag( rvalue );
    %clear rvector rvalue
    disp( 'Calculated Eigen Vectors & Eigen Values of CM' );
    [sorted_evalue, index] = sort( evalue, 'descending' );
    %Now rearrange eigenvectors in the order of rearranged eigen values
    if nof ~= length(index)
      error( sprintf('nof found to be %d, needs to match number of indices = %d', nof, length(index)) );
    end
    evector( :, 1:nof ) = evector ( :, index );
      %sorted-evalue are in descending order. Are you *sure* you want to take a fraction
      %of the largest of them and name that as "smallest_evalue" ??
      smallest_evalue = (1/100) * sorted_evalue(1);            % to obtain the effective eigen values
      %What is the point of this loop? If it is to find the _second_ location where an eigen value
      %is less than 1/100 of the maximum value, then there would be much more straightfoward
      %ways of doing this
      for i = 1:nof
          if (sorted_evalue(i) < smallest_evalue )
              break;
          end
          %and why the heck is evalue left alone if the largest eigenvalue is negative
          %but cleared otherwise? Because the only way that
          % sorted_evalue(1) < sorted_evalue(1)/100 immediately is if sorted_evalue(1) < 0
          evalue = [ ];
      end
      %and if we reached the end of the loop without using the "break" then is it
      %truly okay that index will point past all of the values??
      index = i+1;
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