       Re: Question: Compile in Mathematica 8.0

• To: mathgroup at smc.vnet.net
• Subject: [mg114704] Re: Question: Compile in Mathematica 8.0
• From: Patrick Scheibe <pscheibe at trm.uni-leipzig.de>
• Date: Mon, 13 Dec 2010 03:54:31 -0500 (EST)

```Hi,

the situation is simple. What should the compiler assume, when it sees
something like this:

len = n*(n - 1)/2

Is it in any case an Integer? No. So lets give Compile a hint, that we
want len to be an integer:

Compile[{{n, _Integer}},
Module[
{len = 0},
len = n*(n - 1)/2;
]
]

and now Compile tell us instantly:

Compile::cset: "Variable len of type \!\(\"_Integer\"\) encountered in
assignment of type \!\(\"_Real\"\)."

So what you want is maybe:

v1 = Compile[{{n, _Integer}}, Module[
{g, len = 0},
len = Quotient[n*(n - 1), 2];
g = RandomVariate[NormalDistribution[0., 1.], len]]]

and everthing is fine.

In:= v1

Out= {0.884713, 0.228091, 0.874789}

Hope this helps.

Cheers
Patrick

On Sat, 2010-12-11 at 01:52 -0500, Asim wrote:
> Hi
>
> I am not sure why the first function named v works and why the second
> function named v1 does not compile. The only difference between the
> two functions is in the variable called len which controls the number
> of random numbers that are generated.
>
> I am using Mathematica 8.0 on Windows Vista machine.
>
> Thanks
>
> Asim
>
>
>
> First function:
>
>
> v = Compile[{{n, _Integer}},
>   Module[
>    {g, len},
>    len = n*(n - 1);
>    g = RandomVariate[NormalDistribution[0., 1.], len]
>    ]
>   ]
>
> Output is
>
> CompiledFunction[{n},Module[{g,len},len=n
> (n-1);g=RandomVariate[NormalDistribution[0.,1.],len]],-CompiledCode-]
>
> v
>
> {0.0866864,-0.271121,-0.431317,-0.6787,-1.29246,0.550486}
>
> Second Function:
>
> v1 = Compile[{{n, _Integer}},
>   Module[
>    {g, len},
>    len = n*(n - 1)/2;
>    g = RandomVariate[NormalDistribution[0., 1.], len]
>    ]
>   ]
>
> CompiledFunction[{n},Module[{g,len},len=1/2 n
> (n-1);g=RandomVariate[NormalDistribution[0.,1.],len]],-CompiledCode-]
>
> v1
>
> During evaluation of In:= CompiledFunction::cfse: Compiled
> expression {-0.325949,1.72381,0.368231} should be a machine-size
> integer. >>
>
> During evaluation of In:= CompiledFunction::cfex: Could not
> complete external evaluation at instruction 8; proceeding with
> uncompiled evaluation. >>
>
> Out= {0.295626, 0.664446, 0.654626}
>
>
>
>

```

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