Re: Passing CompiledFunction to Java
- To: mathgroup at smc.vnet.net
- Subject: [mg38756] Re: [mg38707] Passing CompiledFunction to Java
- From: Todd Gayley <tgayley at wolfram.com>
- Date: Wed, 8 Jan 2003 04:13:38 -0500 (EST)
- Sender: owner-wri-mathgroup at wolfram.com
At 02:42 AM 1/6/03, Reinhard Oldenburg wrote:
>Is it possible to pass a CompiledFunction from Mathematica
>to Java via J/Link?
>My basic problem is that I use symbolic methods to build functions
>that have to be evaluated many times within the Java part
>of my program, thus speed is the main objective. Any other suggestions?
>
>Yours,
>Reinhard Oldenburg
Reinhard,
I presume that you are _not_ asking whether you can pass a CompiledFunction
to Java and then execute it entirely within the Java runtime. That is not
possible--to call the CompiledFunction with some arguments you must call
back to Mathematica.
To pass a CompiledFunction to Java, use J/Link's Expr class, which can
store any Mathematica expression. If you have a method that takes an Expr
argument, then you can pass anything for that argument slot from
Mathematica. Say you have a Java method like this:
private Expr storedExpr;
public void storeThisExpr(Expr e) {
storedExpr = e;
}
You can call this from Mathematica like this:
In[100]:= cf = Compile[....];
In[101]:= obj@storeThisExpr[cf]
If you are manually reading the CompiledFunction from a link, use the
getExpr() method:
Expr e = ml.getExpr();
No matter which way you get the CompiledFunction into Java as an Expr, to
call back to Mathematica to execute it you have to use a relatively obscure
sequence of MathLink calls. You cannot use putFunction() because the head
is not a symbol--it's the expression CompiledFunction[...]. You must
manually build the expression from a head and arguments. Here is the code:
// Assume e is an Expr containing a CompiledFunction that
// you want to call with the argument 42.
ml.putNext(MathLink.MLTKFUNC);
ml.putArgCount(1);
// Next we put the head
ml.put(e);
// Then the arguments
ml.put(42);
ml.waitForAnswer();
// Now read the answer ...
Having said all this, do you really need to pass the CompiledFunction
itself to Java? Why not just send its name to Java (i.e., assign the
function to a symbol and then pass the symbol name to Java)? Let the
CompiledFunction live only in Mathematica and just refer to it by name from
your Java code.
Todd Gayley
Wolfram Research