PARFOR loop: The entire array or structure 'H' is a broadcast variable.This might result in unnecessary communication overhead.

clear all

clc

% file_name11 = ('enter DEM filename');
% filename1 = input(file_name11,'s');

DEMdata = importdata ('28_32_94_98_arc.txt',' ',6);

H=DEMdata.data;      %BOLD% %%size of H=14400X14400

% [NHrow NHcol] = size(H);

% Resultt = zeros(NHrow,NHcol);

% Resultt=Resultt-9999;

%  lat0 = input('minimum latitude');

%  lat1 = input ('maximum latitude');

%  lon0 = input ('minimum longitude');

%  lon1 = input ('maximum longitude');

% H_res_deg = (lat1-lat0)/NHrow;

% res_m = 1000* (111.1949*(H_res_deg));    % resolution in meters = deltax = deltay

%  s_cap_m = input('Enter the radius of integration (in meters)');  %in meters (inner radius

% s_cap_m = 8000;

% np = ceil(s_cap_m/res_m);

% if mod(np,2)==0

%     aaa=1;

% else

%     aaa=0;

% end

% some constant matrices x1, x2, y1, y2

href=0;

parfor i = 1780:12620

      i

      for j = 1780:12620

    %%%%%%%%%H is the broadcast variable

          hh = H(i-np:i+np,j-np:j+np);  %BOLD%

          %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
          h = H(i,j)-hh;

       Resultt(i,j) = somefunction(x1,x2,y1,y2,href,h);
      end
  end

Answer 1

[Walter Roberson]

This happens when the parfor body needs to access multiple rows and multiple columns of a variable relative to the parfor index.

There are workarounds for simpler cases.

Suppose that the code needed K = H(i-1:i, :) then you could write

H1 = H(1:end-1, :);
H2 = H(2:end,:);

before the loop, and then inside the loop you would

K = [H1(i, :), H2(i, :) ];

Here, H1 and H2 would each only need one row of and so could each be sliced.

As you have a variable number of rows and columns accessed you cannot write your code in terms of individual variables, but you could perhaps work something out with cell array.

(As usual though it is better to slice by multiple rows than multiple columns.)

[ropesh goyal]

Thank you Walter for your answer. This seems a great idea and will probably work.

I was just trying something, like declaring a temporary variable let say 'w' = H; just between parfor i=1780:12620 and for j=1780:12620 and then using hh=w(i-np:i+np,j-np:j+np).

It also eliminated the warning of communication overhead.

What you suggest??

[Walter Roberson]

I would tend to think that would have the same problems.

[ropesh goyal]

Ok... Thank you for your time