4
$\begingroup$

The following code makes mathematica print "ParallelTable::nopar1: [...] cannot be parallelized; proceeding with sequential evaluation."

(*Exit[]*)
Subscript[r, 1] = Abs[x + y I];
Subscript[r, 2] = Abs[x + y I - a];
plots = ParallelTable[
   ContourPlot[{Abs[Subscript[r, 1]]/Abs[Subscript[r, 2]] == 
        Subscript[c, 1], 
       Subscript[c, 2] == 
        Abs[Subscript[r, 2]] - Abs[Subscript[r, 1]]} /. a -> 5 // 
     Evaluate, {x, -6, 6}, {y, -6, 6}, 
    FrameTicks -> {Range[-6, 6, 1], Range[-6, 6, 1], None, 
      None}], {Subscript[c, 1], 0, 2, 0.1}, {Subscript[c, 2], -2, 2, 
    0.2}];
Animate[plots[[i]][[j]], {i, 1, Length[plots], 1}, {j, 1, 
  Length[plots[[1]]], 1}]

Why does this happen even when the expression in ParallelTable can be easily evaluated for any values of $c_1$ and $c_2$ ?

Note: "Right Click> convert to StandardForm" will make the subscripts readable.

$\endgroup$
  • $\begingroup$ This works r1 = Abs[x + y I]; r2 = Abs[x + y I - a]; plots = ParallelTable[ ContourPlot[{Abs[r1]/Abs[r2] == c1, c2 == Abs[r2] - Abs[r1]} /. a -> 5 // Evaluate, {x, -6, 6}, {y, -6, 6}, FrameTicks -> {Range[-6, 6, 1], Range[-6, 6, 1], None, None}], {c1, 0, 2, 0.1}, {c2, -2, 2, 0.2}]; $\endgroup$ – chris Nov 16 '12 at 9:13
7
$\begingroup$

It seems Mathematica does not like subscript variables for ParallelTable So if you define

r1 = Abs[x + y I];
r2 = Abs[x + y I - a];

then

plots = ParallelTable[
   ContourPlot[{Abs[r1]/Abs[r2] == c1, c2 == Abs[r2] - Abs[r1]} /. 
      a -> 5 // Evaluate, {x, -6, 6}, {y, -6, 6}, 
    FrameTicks -> {Range[-6, 6, 1], Range[-6, 6, 1], None, None}, 
    ContourStyle ->{{ColorData[10][c1*5]}, 
    Directive[Dashed, ColorData[10][(c2 + 2)*2.5]]}], {c1, 0, 2, 0.1}, {c2, -2, 2,
     0.2}];

produces

plots // Flatten // Show

Mathematica graphics

$\endgroup$
  • $\begingroup$ Thanks, that seems to work. Is there any real reason why mathematica fails to parallelize when there are subscripts? $\endgroup$ – Navin Nov 16 '12 at 14:21
  • 1
    $\begingroup$ @Navin this I don't know. Parallelize is still a fragile beast AFAIK. $\endgroup$ – chris Nov 16 '12 at 15:12

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.