What exactly prevents this code from compiling?

Question

I am trying to compile a function that operates on an initial array (doing some sequential operation) to produce a matrix (which consists of N iterations of the initial array).

Below is a minimal working example:

NT = 10^1; NM = 2;
minitial = 2 RandomInteger[{}, NM] - 1.;
mzero = ConstantArray[0, {NT, NM}];
networkStep = 
  Compile[{{minitial, _Integer, 
     1}, {NT, _Integer}, {NM, _Integer}, {mzero, _Real, 2}}, 
   Block[{md = minitial, moo = mzero}, 
    Rescale@Table[
      Do[md[[j]] = Sign[RandomReal[{-1, 1}]], {j, Range@NM}]; 
      moo[[i, ;;]] = md, {i, 1, NT}]]];
mm = networkStep[minitial, NT, NM, mzero]

What prevents this function from compiling? Everything seems localized and appropriately defined to me.

Rescale isn't compilable: https://mathematica.stackexchange.com/a/1101/1871 ;; (whose FullForm is 1;;All) cannot be compiled, either: https://mathematica.stackexchange.com/a/61651/1871 — xzczd, Dec 24 '20 at 07:57
Thank you - replacing ;; with All fixed the problem. Rescale seems like it can't be compiled but it does compile and speeds things up. — anon248, Dec 24 '20 at 10:10
Rescale results in a MainEvaluate in the output of CompilePrint, but given it's called only once, it doesn't cause significant slowing down. — xzczd, Dec 24 '20 at 10:25

score 3 · Accepted Answer · answered Dec 24 '20 at 10:15

Based on xzczd's comment, replacing ";;" with "All" in the code fixed the compilation problem (Rescale does not pose a problem):

NT = 10^5; NM = 2;
minitial = 2 RandomInteger[{}, NM] - 1.;
mzero = ConstantArray[0, {NT, NM}];
networkStep = 
  Compile[{{minitial, _Integer, 
     1}, {NT, _Integer}, {NM, _Integer}, {mzero, _Real, 2}}, 
   Block[{md = minitial, moo = mzero}, 
    Rescale@Table[
      Do[md[[j]] = Sign[RandomReal[{-1, 1}]], {j, Range@NM}];
      moo[[i, ;;]] = md, {i, 1, NT}]], CompilationTarget -> "C"];
mm = AbsoluteTiming[networkStep[minitial, NT, NM, mzero]]; mm[[1]]

gives

1.11684 seconds

while

NT = 10^5; NM = 2;
minitial = 2 RandomInteger[{}, NM] - 1.;
mzero = ConstantArray[0, {NT, NM}];
networkStep = 
  Compile[{{minitial, _Integer, 
     1}, {NT, _Integer}, {NM, _Integer}, {mzero, _Real, 2}}, 
   Block[{md = minitial, moo = mzero}, 
    Rescale@Table[
      Do[md[[j]] = Sign[RandomReal[{-1, 1}]], {j, Range@NM}];
      moo[[i, All]] = md, {i, 1, NT}]], CompilationTarget -> "C"];
mm = AbsoluteTiming[networkStep[minitial, NT, NM, mzero]]; mm[[1]]

gives 0.025396 seconds.

What exactly prevents this code from compiling?

1 Answers1