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Non-numeric arguments to Compile-d functions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg82117] Non-numeric arguments to Compile-d functions
  • From: "Andrew Moylan" <andrew.j.moylan at gmail.com>
  • Date: Fri, 12 Oct 2007 03:02:15 -0400 (EDT)

Here's a compiled function that does some (made-up) operation on a
real-valued function f:

Compile[{},
 Do[If[f[i] < 0, Return[{i, f[i]}]], {i, 10}],
 {{f[_], _Real}}
]

(It finds the first integer i such that f[i] is negative.)

For the usual reasons of modularity, I would like to make compiled functions
like this not refer to global variables named f. (We can't put f as one of
the elements of the first argument to compile, because those must all be
numeric scalars or arrays.)

Here's one way to do this:

Module[
 {f, compiledpart},

 compiledpart = Compile[{},
   Do[If[f[i] < 0, Return[{i, f[i]}]], {i, 10}],
   {{f[_], _Real}}
   ];

 findfirstnegative[tempf_] := (compiledpart /. f -> tempf)[]
]

I don't really like this solution because we needed to use two names (f and
tempf). Using two names per argument could get messy if there are several
non-numeric arguments instead of just f.

Is this the recommended method for compiling "as much of a function as
possible"?

Note that the following attempt (which doesn't need a tempf) doesn't work:

With[{rhs = compiledpart}, findfirstnegative[f_] := rhs]

It fails because Mathematica automatically renames the f in the
CompiledFunction in compiledpart to *avoid* the very naming clash I am
trying to create. The With statement effectively creates:

findfirstnegative[f$_] := CompiledFunction[{},
  Do[If[f$851[i]<0, Return[{i,f$851[i]}]], {i,10}],
  -CompiledCode-
]

What's the neatest, "right" way to make compiled functions that take
non-numeric arguments?



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