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May 30, 2011, 6:33:58 AM5/30/11

to

I'd like to compile a function that estimates (assuming a spherical

earth) the length of a degree of longitude at any particular

latitude. Here's how I write it up and test its speed:

earth) the length of a degree of longitude at any particular

latitude. Here's how I write it up and test its speed:

In[1]:= radiusOfEarth=6378100.;

latitudeDegreeLength=2*Pi*radiusOfEarth/360

Out[2]= 111319.

In[3]:= X=Table[RandomReal[{0,90}],{100000}];

In[4]:=

GetLongitudeDegreeLength=Compile[{latitude},latitudeDegreeLength*Cos[latitude

Degree]]

Out[4]= CompiledFunction[{latitude},latitudeDegreeLength Cos[latitude

=B0],-CompiledCode-]

In[5]:= Timing[Map[GetLongitudeDegreeLength,X];]

Out[5]:= {0.312,Null}

Since the values of "latitudeDegreeLength" and "Degree" are constant,

I'd prefer to use numerical approximations in the definition so the

compiled code doesn't have to request the values of these global

variables at runtime. Like this:

In[6]:= GetLongitudeDegreeLength=Compile[{latitude},

111318.*Cos[0.0174532925 latitude]]

Out[6]:= CompiledFunction[{latitude},111318. Cos[0.0174533 latitude],-

CompiledCode-]

In[7]:= Timing[Map[GetLongitudeDegreeLength,X];]

Out[7]:= {0.031,Null}

Is there any way to tell Mathematica that I'd like these symbols to be

evaluated before the compilation so that I don't have to copy and

paste the numerical values into the definition?

Thanks.

May 30, 2011, 7:48:12 AM5/30/11

to

there are several, but for this case I think With is probably the clearest:

radiusOfEarth=6378100.;

With[{latitudeDegreeLength=2*Pi*radiusOfEarth/360,deg=N[Degree]},

GetLongitudeDegreeLength=Compile[{latitude},

latitudeDegreeLength*Cos[latitude*deg]]

]

hth,

albert

May 31, 2011, 7:46:02 AM5/31/11

to

Thank you!

May 31, 2011, 7:49:03 AM5/31/11

to

Dear MathGroup members,

After reading this question, I started wondering if there is any way to

receive warnings that there might be something "wrong" with a compiled

function (e.g. that Mathematica might drop back to standard evaluation

instead of running compiled code).

CCodeGenerate[] does issue some warnings:

CCodeGenerate[GetLongitudeDegreeLength, "fun"]

CCodeGenerate::wmreq: "The expression

Function[{latitude},latitudeDegreeLength] requires Mathematica to be

evaluated. The function will be generated but can be expected to fail

with a nonzero error code when executed"

Is there a way to get some similar warnings from Compile[]? It is not

obvious and intuitive that using an e.g. elsewhere defined constant

might slow down a compiled function to non-compiled speed.

GetLongitudeDegreeLength =

Function[{latitude}, latitudeDegreeLength*Cos[latitude Degree]]

Timing[Map[GetLongitudeDegreeLength,X];]

is only 1.5 slower on my machine than the compiled version (with

non-inlined constants). (I know that Map can auto-compile its argument,

but setting SetSystemOptions["CompileOptions" -> "MapCompileLength" ->

Infinity] doesn't seem to change anything here, so I assume that the

timing is valid for the uncompiled case)

Jun 1, 2011, 4:30:16 AM6/1/11

to

On 2011.05.30. 12:33, Ben wrote:

After reading up a bit more on Compile[] based on Oliver's replies, I

came across another possible solution, which you might find interesting:

GetLongitudeDegreeLength =

Compile[{{latitude, _Integer, 0}},

latitudeDegreeLength*Cos[latitude Degree],

CompilationOptions -> {"InlineExternalDefinitions" -> True}]

This is documented at ref/CompilationOptions and

Compile/tutorial/Operation

-- Szabolcs

Jun 1, 2011, 4:34:31 AM6/1/11

to

On Tue, 31 May 2011, Szabolcs Horv=E1t wrote:

> Dear MathGroup members,

>

> After reading this question, I started wondering if there is any way to

> receive warnings that there might be something "wrong" with a compiled

> function (e.g. that Mathematica might drop back to standard evaluation

> instead of running compiled code).

>

> CCodeGenerate[] does issue some warnings:

>

> CCodeGenerate[GetLongitudeDegreeLength, "fun"]

>

> CCodeGenerate::wmreq: "The expression

> Function[{latitude},latitudeDegreeLength] requires Mathematica to be

> evaluated. The function will be generated but can be expected to fail

> with a nonzero error code when executed"

>

> Is there a way to get some similar warnings from Compile[]? It is not

> obvious and intuitive that using an e.g. elsewhere defined constant

> might slow down a compiled function to non-compiled speed.

>

> GetLongitudeDegreeLength =

> Function[{latitude}, latitudeDegreeLength*Cos[latitude Degree]]

> Timing[Map[GetLongitudeDegreeLength,X];]

>

> is only 1.5 slower on my machine than the compiled version (with

> non-inlined constants). (I know that Map can auto-compile its argument,

> but setting SetSystemOptions["CompileOptions" -> "MapCompileLength" ->

> Infinity] doesn't seem to change anything here, so I assume that the

> timing is valid for the uncompiled case)

>

>> Thanks.

>>

>

>

>

Hi,

does this help?

f[x_] := x + 1

f1 = Compile[{{x, _Integer, 0}}, f[x]]

f1[1]

<< "CompiledFunctionTools`"

CompilePrint[f1]

System`SetSystemOptions[

"CompileOptions" -> "CompileReportExternal" -> True];

f2 = Compile[{{x, _Integer, 0}}, f[x]]

Oliver

Jun 1, 2011, 4:34:42 AM6/1/11

to

2011/5/31 Oliver Ruebenkoenig <rueb...@wolfram.com>:

>

> Hi,

>

> does this help?

>

> f[x_] :== x + 1

> f1 == Compile[{{x, _Integer, 0}}, f[x]]

>

> f1[1]

>

>

> << "CompiledFunctionTools`"

>

> CompilePrint[f1]

>

> System`SetSystemOptions[

> =C2 "CompileOptions" -> "CompileReportExternal" -> True];

>

> f2 == Compile[{{x, _Integer, 0}}, f[x]]

>

>

> Hi,

>

> does this help?

>

> f[x_] :== x + 1

> f1 == Compile[{{x, _Integer, 0}}, f[x]]

>

> f1[1]

>

>

> << "CompiledFunctionTools`"

>

> CompilePrint[f1]

>

> System`SetSystemOptions[

>

> f2 == Compile[{{x, _Integer, 0}}, f[x]]

>

Thank you, that's exactly what I've been looking for (I think)!

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