error with 'parfor' in matlab

Question

i have written a function in matlab, which is to calculate a cost function for an array:

  function [F1val, Com]=F1(Community,NeighMat)  
        global FlattedAdjMat;
        Com=zeros(numel(Community),3);
        Com(:,1)=Community';  % The First row of Com= Community's Nodes  
        % Calculating INTERNAL Edges of Community  
            for j=1:numel(Com(:,1))
                Com(j,2)=sum(FlattedAdjMat((Community),Com(j,1)));% Internal Degrees of Node j            
            end
        F1val=(nansum(Com(:,3)./((Com(:,2)+Com(:,3)))));
  end

But i have 2 problem with the line Com(j,2)=sum(FlattedAdjMat((Community),Com(j,1))),

1. when i try to execute it in parallel using parfor:

   parfor iii=1:5
       [z,p]=F1(Community,NeighMat)
   end
   

   this error occurs in the line: Index exceeds matrix dimensions while in normal case(not Parallel) there is no problem

2. it is very time consuming and slow down the speed.

NeighMat is a weighted adjacency matrix, Community is an array of the matrix indexes, FlattedAdjMat is adjacency matrix.

whould you please help me?

sample data:

for ii=1:10
   NeighMat{ii}=randi(10,1,10)
end

Community=[1,5,6,8,9];`

global FlattedAdjMat
FlattedAdjMat=randi([0,1],10,10)

Answer 1

You have a problem with global variable. This problem is well discussed here.

I rewrite Your code a bit and it works for me perfect (Matlab 2017b Win64)

close all
clear all
clc
%% SAMPLE DATA
for ii=1:10
    NeighMat{ii}=randi(10,1,10);
end
Community=[1,5,6,8,9];
FlattedAdjMat=randi([0,1],10,10);
%% BODY
parfor iii=1:5
    [z,p]=F1(Community,NeighMat,FlattedAdjMat)
end

%% FUNCTION
function [F1val, Com]=F1(Community,NeighMat,FlattedAdjMat)
    Com=zeros(numel(Community),3);
    Com(:,1)=Community';  % The First row of Com= Community's Nodes
    % Calculating INTERNAL Edges of Community
    for j=1:numel(Com(:,1))
        Com(j,2)=sum(FlattedAdjMat((Community),Com(j,1)));% Internal Degrees of Node j
    end
    F1val=(nansum(Com(:,3)./((Com(:,2)+Com(:,3)))));
end