[PYTHON MATRIX-SIG] LAPACK module questions

[Doug Heisterkamp]

''
> 
> 
> I'm probably the only one here who can answer these questions (yes I
> know that documentation for the C API would be nice).
> 
> First a question.  Are you building this on top of Guido's bgen tool?
> I really think that this is the right way to go.  Hopefully bgen can
> be eventually turned into a nice generic tool for specifying
> interfaces to any C/FORTRAN library.  It already handles a large
> collection of interface specifications.  It has the very nice modular
> design of one automatic part that tries to extract the interface
> definition which produces interface definition files that can be
> easily edited by the user for the cases where it guesses wrong.
> Adding array objects to bgen would not be a whole lot of work (so many
> things I'd like to do if I just had a free 10 hours or so).

Unfortunately, I did not use bgen.  I'll take a look at to see what it
can do.

> 
> I think that creating a raw C level binding to these libraries is the
> right thing to do, and then to write a python module that provides a
> nice friendly interface on top of the raw functions created in the
> module.  The basic point here is that this should be doable without
> writing any C code.
> 
> I'd be interested in seeing a copy of what you've done so far.

I'll place a copy on the ftp server here at unl.  I'll make some of the
changes from below before placing it there.  I'll let the list know when
it's placed on the server and it actual location.

Doug

> 
> Arrays are not part of the abstract object interface.  The right way
> to write a function that takes in a single argument and passes it on
> to a C function expecting a 1d array of doubles and returning a 1d
> array of doubles is as follows:
> 
> static PyObject *function(PyObject *ignored, PyObject *args) {
>   PyArrayObject *ap, *apr;
>   PyObject *op;
>   int n;
> 
>   TRY(PyArg_ParseTuple(args, "O", &op));
>   TRY(ap = (PyArrayObject *)PyArray_ContiguousFromObject(op, PyArray_DOUBLE, 1, 1));
> 
>   n = ap->dimensions[0];
> 
>   TRY(apr = (PyArrayObject *)PyArray_FromDims(1, &n, PyArray_DOUBLE));
> 
>   c_function((double *)ap->data, (double *)apr->data, n)  
> 
>   Py_DECREF(ap);  /* Needed because PyArray_ContiguousFromObject INCREFs it. */
> 
>   return (PyObject *)apr;
> }
> 
> In fact, if there is an error in allocating the return array this will
> leak memory, but I figure anytime you're getting exceptions during
> array allocation, enough things are wrong with your system that a
> little memory leak won't be a problem.
> 
> Hopefully from the general complexity of this you can see the value in
> a bgen style approach.
> 
> -Jim
> 


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