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Re: Problem with compile fct. and Thread

  • To: mathgroup at smc.vnet.net
  • Subject: [mg124578] Re: Problem with compile fct. and Thread
  • From: "Oleksandr Rasputinov" <oleksandr_rasputinov at hmamail.com>
  • Date: Wed, 25 Jan 2012 07:06:19 -0500 (EST)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <jfm01p$js0$1@smc.vnet.net>

On Tue, 24 Jan 2012 10:10:01 -0000, kristoph <kristophs.post at web.de> wrote:

> Hi
>
> I get an error when trying to compute the following "toy" code:
>
> (*the compile function*)
> test=Compile[{{bw,_Real},{regData,_Real,1},{leg,_Integer}},
> Module[{h,tab2,xMat},
> h=1;
> tab2=Table[(regData[[i]]-regData[[j]]),{i,1,leg},{j,1,leg}];
> xMat=Thread[{1.,tab2[[h]]}]
> ]
> ,CompilationOptions->{"InlineExternalDefinitions"->True}];
>
> (*generating random sample data*)
> leg=100;
> data=RandomReal[{0,1},leg];
> bw=.1;
>
> (*using the compile function with the above generated data, produces
> the error*)
> test[bw, data, leg]
>
> The function "test" works fine if I construct the matrix "xMat" using
> the function Table. However, I prefer Thread because it is twice as
> fast.
>
> I just do not see where my mistake is. I do appreciate any
> suggestions. Thanks in advance.
> Cheers,
> Kris
>

The problem again is with the types of various expressions, but this time  
it is caused by a call out of the compiled code in evaluating Thread[...].  
In such cases one must explicitly specify the return type one expects for  
expressions matching a given pattern using the third argument of Compile,  
which in this case should be {{_Thread, _Real, 2}}:

test = Compile[
  {{bw, _Real}, {regData, _Real, 1}, {leg, _Integer}},
  Module[{h = 1, tab2 = {{0., 0.}}, xMat = {{0., 0.}}},
   tab2 = Table[
    regData[[i]] - regData[[j]],
    {i, 1, leg}, {j, 1, leg}
   ];
   xMat = Thread[{1., tab2[[h]]}]
  ], {{_Thread, _Real, 2}},
  CompilationOptions -> {"InlineExternalDefinitions" -> True}
];

A better way to write it is to avoid the call out of compiled code  
altogether. There also isn't any reason to use xMat here and it introduces  
a needless copy operation on the final result, so one may as well remove  
this too, ending up with the following:

test2 = Compile[
  {{bw, _Real}, {regData, _Real, 1}, {leg, _Integer}},
  Module[{h = 1, tab2 = {{0., 0.}}},
   tab2 = Table[
    regData[[i]] - regData[[j]],
    {i, 1, leg}, {j, 1, leg}
   ];
   Transpose[{
    ConstantArray[1., Length@tab2[[h]]],
    tab2[[h]]
   }]
  ], CompilationOptions -> {"InlineExternalDefinitions" -> True}
];

As is probably clear by now, the use of compiled code is not without its  
difficulties. (Also, incidentally, "InlineExternalDefinitions" -> True  
doesn't serve any purpose for this example, but I left it in anyway.)



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