How to convert for loop to parfor?

I need to make my code faster and I am trying to convert for loops into parfor. Often I see this message: "the entire array or structure is a broadcast variable. This might result in unnecessary communication overhead". The code runs, but takes the same time as with for loops. How could I convert my code below? The message appears for variables 'elements' and 'nodes' (here I wrote only the first 20 rows for them).

nodes=load('nodes.txt');
elements=load('elements.txt');
nel=size(elements,1);
parfor i=1:nel
      nodes_el=elements(i,3:5);
      coor_el=nodes(nodes_el,2:3);
      X=coor_el(:,1);
      Y=coor_el(:,2);
      trian=polyshape(X,Y);
      [bx,by]=centroid(trian);
      cx(i)=bx;
      cy(i)=by;
      Area(i)=polyarea(X,Y);
  end

elements.txt
1  1  2  3  63
2  1  4  5  64
3  1  6  7  65
4  1  8  9  66
5  1  9  10  67
6  1  10  11  68
7  1  12  13  69
8  1  14  15  70
9  1  16  17  18
10  1  18  19  71
11  1  20  21  72
12  1  22  23  73
13  1  24  25  74
14  1  26  27  28
15  1  28  29  75
16  1  30  31  76
17  1  32  33  77
18  1  34  35  78
19  1  36  37  38
20  1  38  39  79

nodes.txt.

1  55.0000000  50.0000000
2  56.8750000  50.0000000
3  58.7500000  50.0000000
4  60.6250000  50.0000000
5  62.5000000  50.0000000
6  64.3750000  50.0000000
7  66.2500000  50.0000000
8  68.1250000  50.0000000
9  70.0000000  50.0000000
10  73.7500000  50.0000000
11  77.5000000  50.0000000
12  81.2500000  50.0000000
13  85.0000000  50.0000000
14  88.7500000  50.0000000
15  92.5000000  50.0000000
16  96.2500000  50.0000000
17  100.0000000  50.0000000
18  100.0000000  55.0000000
19  100.0000000  60.0000000
20  100.0000000  65.0000000

Answer 1

[Shashank]

Hi pasquale,

I think in your case there will not be any speed up if you use 'parfor' since the statements in the 'for' loop are dependent on the previous one.

For example,

coor_el=nodes(nodes_el,2:3);

is dependent on calculating 'nodes_el' which is done in the previous statement:

nodes_el=elements(i,3:5);

For more information on this, refer to the following documentation link

Convert for-Loops Into parfor-Loops

- Shashank

[Pasquale]

Ok, thanks. Can I ask you if another problem can be solved? When I try to convert for to parfor loop, I see also this message: "the temporary variable is used after the parfor loop, but its value is not available after the loop".