Re: calling Fortran code from Lisp

Tamas K Papp wrote:
> On Fri, Apr 06, 2007 at 05:11:27PM -0400, Raymond Toy wrote:
>   
>>>>>>> "Tamas" == Tamas K Papp <Tamas> writes:
>>>>>>>               
>>     Tamas> Hi,
>>     Tamas> Is it possible to call a Fortran subroutine from Lisp?  I have seen
>>     Tamas> the C language FFI in the docs, but I wonder if it would be possible
>>     Tamas> to call Fortran somehow.  There is a subroutine for banded sparse
>>     Tamas> matrices in LAPACK I would like to use.
>>
>> As mentioned by others, there are already libraries that can do this.
>> If you want to cook your own, you do need to exercise some care.  All
>> Fortran compilers I know of have, essentially, a C-compatible
>> interface.  The only thing you need to know about is how Fortran
>> handles strings.  
>>
>> If the existing libraries don't do what you want, please ask again
>> here, and we can help with setting up a call to a Fortran routine.
>>     
>
> Hi Raymond,
>
> First, a short explanation why I am not using the existing libraries:
> I need the ability to reshape a more than 2 dimensional array into a
> matrix, do some matrix manipulation (eg matrix product, solving linear
> system), reshape the result into an array, etc.  I don't know how to
> do this in either Matlisp or rfi's libraries.
>
>   
Matlisp only handles 2-D matrices.  You can mix and match Lisp arrays 
and Matlisp matrices, with some care.
> I tried calling dgemm to do a simple matrix multiplication first.
> Fortunately Atlas has a C interface, so I can use that.  But I got
> stuck because I don't know how to extract the pointer of a simple
> array, the sys:vector-sap mentioned in the user's guide doesn't work
> here.  What should I use instead?
>
>   
vector-sap only works on specialized arrays.  For other array types, you 
need to get to the actual storage area that hold the data.  
(%array-data? or with-array-data?)  Once you have that object, 
vector-sap will do what you want.
> If you have any advice on what to do, or how to improve this code in
> other ways, please tell me.
>
>
>   
[snip code]

What happens when you run this code?  I can't easily run this myself 
right now.
One note, however.  LAPACK matrices are in column-major order but Lisp 
is row-major order.  You might need to transpose your matrices before 
calling LAPACK routines.  This is why Matlisp stores its matrices as a 
1D vector internally.  Perhaps the C interface doesn't need this.

Ray