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Subject: [Ocaml and C] Passing Arrays and Matrices of floats from Ocaml to C 
	and back
From: Odalric-Ambrym Maillard <odalricambrym.maillard@gmail.com>
To: caml-list@inria.fr
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<caml-list@inria.fr>,


Hello, I have the following problem : I wan to use a Least-squares
Regression solver written in C in a program written in OCaml.

I have something like this in the Ocaml program,
*
let beta = solve_olsr psi_matrix y_train in ...*

where psi_matrix is built using  Array.make_matrix and y_train by Array.make

The dimensions are KxN for psi_matrix and N for y_train, and the output beta
should be a vector of length K (built with Array.make etc).

I have a C function with the following signature :
*
void  olsr(int rows, int columns,
         double **matrix_of_data,
         double *vector_of_data,
         double ** vector_of_coefficients)*

Thus, I need to create a stub function, that will lok like this

*CAMLValue solve_olsr(value ...,value...) {
 CAMLparam...

 CAMLReturn ...
}*

My problem is the following : how do  proceed since the parameters I need to
transmt are vectors or matrices of float (for Caml, i.e. double for C), and
not just integers or floats ? I really do not know how to transfer arrays
and matrix of floats from Caml to C, and back.


It would be great to have an answer.

Thank you,
Odalric-Ambrym

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&lt;<a href=3D"mailto:caml-list@inria.fr">caml-list@inria.fr</a>&gt;, <br><=
br><br>Hello, I have the following problem : I wan to use a Least-squares R=
egression solver written in C in a program written in OCaml.<br><br>I have =
something like this in the Ocaml program,<br>
<i><br>let beta =3D solve_olsr psi_matrix y_train in ...</i><br><br>where p=
si_matrix is built using=A0 Array.make_matrix and y_train by Array.make <br=
>The dimensions are KxN for psi_matrix and N for y_train, and the output be=
ta should be a vector of length K (built with Array.make etc).<br>
<br>I have a C function with the following signature :<br><i><br>void=A0 ol=
sr(int rows, int columns, <br>=A0=A0=A0 =A0=A0=A0 =A0double **matrix_of_dat=
a, <br>=A0=A0=A0 =A0=A0=A0 =A0double *vector_of_data,<br>=A0=A0=A0 =A0=A0=
=A0 =A0double ** vector_of_coefficients)</i><br>
<br>Thus, I need to create a stub function, that will lok like this<br><br>=
<i>CAMLValue solve_olsr(value ...,value...) {<br>=A0CAMLparam...<br><br>=A0=
CAMLReturn ...<br>}</i><br><br>My problem is the following : how do=A0 proc=
eed since the parameters I need to transmt are vectors or matrices of float=
 (for Caml, i.e. double for C), and not just integers or floats ? I really =
do not know how to transfer arrays and matrix of floats from Caml to C, and=
 back.<br>
<br><br>It would be great to have an answer.<br><br>Thank you,<br>Odalric-A=
mbrym<br><br>

--001485f45454815fa90480f79cae--


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From: Paolo Donadeo <p.donadeo@gmail.com>
Date: Thu, 4 Mar 2010 14:08:17 +0100
Message-ID: <4b5157c31003040508u98111adkc485f89c319f129c@mail.gmail.com>
Subject: Re: [Caml-list] [Ocaml and C] Passing Arrays and Matrices of floats 
	from Ocaml to C and back
To: caml-list@inria.fr
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Did you consider using the bigarray library?

http://caml.inria.fr/pub/docs/manual-ocaml/manual043.html


-- 
Paolo


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On Thu, 4 Mar 2010 12:07:57 +0100, Odalric-Ambrym Maillard wrote:
> 
> Hello, I have the following problem : I wan to use a Least-squares
> Regression solver written in C in a program written in OCaml.

Aren't the Lacaml/LAPACK least square enough ?
http://www.ocaml.info/home/ocaml_sources.html#lacaml

If you want to bind your very own solver, the recommended route is to
use bigarrays :
http://caml.inria.fr/pub/docs/manual-ocaml/manual043.html#toc143

My 0.02¤,
C.


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	 <4b5157c31003040508u98111adkc485f89c319f129c@mail.gmail.com>
Date: Thu, 4 Mar 2010 15:04:34 +0100
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Subject: Re: [Caml-list] [Ocaml and C] Passing Arrays and Matrices of floats 
	from Ocaml to C and back
From: Odalric-Ambrym Maillard <odalricambrym.maillard@gmail.com>
To: Paolo Donadeo <p.donadeo@gmail.com>
Cc: caml-list@inria.fr
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Thanks, I was not aware of this relation between Bigarrays and C.
I will try to use this and tell you of it works as I want.

Odalric

2010/3/4 Paolo Donadeo <p.donadeo@gmail.com>

> Did you consider using the bigarray library?
>
> http://caml.inria.fr/pub/docs/manual-ocaml/manual043.html
>
>
> --
> Paolo
>
> _______________________________________________
> Caml-list mailing list. Subscription management:
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> Bug reports: http://caml.inria.fr/bin/caml-bugs
>



--=20
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Odalric-Ambrym Maillard, Phd student
INRIA Lille - Nord Europe,
- Sequential Learning Project
Institut de Math=E9matiques de Toulouse,
- Equipe de Statistique et Probabilit=E9s
Odalric.maillard@inria.fr,
+33 6.43.71.70.48 (cell)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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Thanks, I was not aware of this relation between Bigarrays and C. <br>I wil=
l try to use this and tell you of it works as I want.<br><br>Odalric<br><br=
><div class=3D"gmail_quote">2010/3/4 Paolo Donadeo <span dir=3D"ltr">&lt;<a=
 href=3D"mailto:p.donadeo@gmail.com">p.donadeo@gmail.com</a>&gt;</span><br>
<blockquote class=3D"gmail_quote" style=3D"border-left: 1px solid rgb(204, =
204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">Did you consider =
using the bigarray library?<br>
<br>
<a href=3D"http://caml.inria.fr/pub/docs/manual-ocaml/manual043.html" targe=
t=3D"_blank">http://caml.inria.fr/pub/docs/manual-ocaml/manual043.html</a><=
br>
<br>
<br>
--<br>
Paolo<br>
<br>
_______________________________________________<br>
Caml-list mailing list. Subscription management:<br>
<a href=3D"http://yquem.inria.fr/cgi-bin/mailman/listinfo/caml-list" target=
=3D"_blank">http://yquem.inria.fr/cgi-bin/mailman/listinfo/caml-list</a><br=
>
Archives: <a href=3D"http://caml.inria.fr" target=3D"_blank">http://caml.in=
ria.fr</a><br>
Beginner&#39;s list: <a href=3D"http://groups.yahoo.com/group/ocaml_beginne=
rs" target=3D"_blank">http://groups.yahoo.com/group/ocaml_beginners</a><br>
Bug reports: <a href=3D"http://caml.inria.fr/bin/caml-bugs" target=3D"_blan=
k">http://caml.inria.fr/bin/caml-bugs</a><br>
</blockquote></div><br><br clear=3D"all"><br>-- <br>~~~~~~~~~~~~~~~~~~~~~~~=
~~~~~~~~~~<br>Odalric-Ambrym Maillard, Phd student<br>INRIA Lille - Nord Eu=
rope,<br>- Sequential Learning Project<br>Institut de Math=E9matiques de To=
ulouse,<br>
- Equipe de Statistique et Probabilit=E9s<br><a href=3D"mailto:Odalric.mail=
lard@inria.fr">Odalric.maillard@inria.fr</a>,<br>+33 6.43.71.70.48 (cell)<b=
r>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~<br>

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Date: Thu, 4 Mar 2010 18:02:50 +0100
Message-ID: <406c33611003040902o897243cled850c2e8184334e@mail.gmail.com>
Subject: Re: [Caml-list] [Ocaml and C] Passing Arrays and Matrices of floats 
	from Ocaml to C and back
From: Odalric-Ambrym Maillard <odalricambrym.maillard@gmail.com>
To: Paolo Donadeo <p.donadeo@gmail.com>
Cc: caml-list@inria.fr
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X-Spam: no; 0.00; ocaml:01 arrays:01 matrices:01 ocaml:01 bigarrays:01 bigarray:01 bigarray:01 stub:01 camlparam:01 val:01 val:01 bigarrays:01 beginner's:01 bug:01 stub:01 

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Using Bigarrays, most of the problem seems to be solved.
However, I still have an important problem:

Now I define in the Ocaml code a matrix (Bigarray.Array2)  "bpsi" and  a
vector (Bigarray.Array1) "by".
Both are defined using the kind Bigarray.float32 and the layout
Bigarray.c_layout.
If I print them in Ocaml, they contains the good values.

Now I call my stub function from Ocaml, written in C: (definef with *
external* ...etc)
*let beta = solve_olsr bpsi by*

In C, I have:

*value solve_olsr(value bpsi, value by){
CAMLparam2(bpsi,by);
int rows = Bigarray_val(bpsi)->dim[0];
int cols = Bigarray_val(bpsi)->dim[1];
...
double * vec_data = Data_bigarray_val(by);
double ** mat_data = Data_bigarray_val(bpsi);
...
print_vector(rows, vec_data);
print_matrix(rows,cols,mat_data);
....*

There are two problems :
 - First, I need to have a matrix defined with type double **, due to the
function I call next, which takes as input a matrix of type double ** and an
array of type double *. I guess that *Data_bigarray_val only* outputs a flat
array corresponding to an Array of any dimension. If this is the case, this
is not what I want (it seems more difficult to allocate a such a contiguous
block in memory when it is big). So is there another function that does the
job, i.e. maps a Bigarray.Array2 to double ** with the right allocation ?
Now, when I print the matrix, the programs crashes (Segmentation fault),
which seems coherent with the previous interpretation.
 - When I print the vector *vec_data*, it has the right number of elements,
but unfortunately all values are 0. Thus I guess there is some problem with
the Bigarray.float32 thing. Is it that ?

Thanks,
Odalric


2010/3/4 Odalric-Ambrym Maillard <odalricambrym.maillard@gmail.com>

> Thanks, I was not aware of this relation between Bigarrays and C.
> I will try to use this and tell you of it works as I want.
>
> Odalric
>
> 2010/3/4 Paolo Donadeo <p.donadeo@gmail.com>
>
> Did you consider using the bigarray library?
>>
>> http://caml.inria.fr/pub/docs/manual-ocaml/manual043.html
>>
>>
>> --
>> Paolo
>>
>> _______________________________________________
>> Caml-list mailing list. Subscription management:
>> http://yquem.inria.fr/cgi-bin/mailman/listinfo/caml-list
>> Archives: http://caml.inria.fr
>> Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
>> Bug reports: http://caml.inria.fr/bin/caml-bugs
>>
>
>
>

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Using Bigarrays, most of the problem seems to be solved.<br>However, I stil=
l have an important problem:<br><br>Now I define in the Ocaml code a matrix=
 (Bigarray.Array2)=A0 &quot;bpsi&quot; and=A0 a vector (Bigarray.Array1) &q=
uot;by&quot;.<br>
Both are defined using the kind Bigarray.float32 and the layout Bigarray.c_=
layout.<br>If I print them in Ocaml, they contains the good values.<br><br>=
Now I call my stub function from Ocaml, written in C: (definef with <i>exte=
rnal</i> ...etc)<br>
<i>let beta =3D solve_olsr bpsi by</i><br><br>In C, I have:<br><br><i>value=
 solve_olsr(value bpsi, value by){<br>CAMLparam2(bpsi,by);<br>int rows =3D =
Bigarray_val(bpsi)-&gt;dim[0];<br>int cols =3D Bigarray_val(bpsi)-&gt;dim[1=
];<br>
...<br>double * vec_data =3D Data_bigarray_val(by);<br>double ** mat_data =
=3D Data_bigarray_val(bpsi);<br>...<br>print_vector(rows, vec_data);<br>pri=
nt_matrix(rows,cols,mat_data);<br>....</i><br><br>There are two problems : =
<br>
=A0- First, I need to have a matrix defined with type double **, due to the=
 function I call next, which takes as input a matrix of type double ** and =
an array of type double *. I guess that <i>Data_bigarray_val only</i> outpu=
ts a flat array corresponding to an Array of any dimension. If this is the =
case, this is not what I want (it seems more difficult to allocate a such a=
 contiguous block in memory when it is big). So is there another function t=
hat does the job, i.e. maps a Bigarray.Array2 to double ** with the right a=
llocation ?<br>
Now, when I print the matrix, the programs crashes (Segmentation fault), wh=
ich seems coherent with the previous interpretation.<br>=A0- When I print t=
he vector <i>vec_data</i>, it has the right number of elements, but unfortu=
nately all values are 0. Thus I guess there is some problem with the Bigarr=
ay.float32 thing. Is it that ?<br>
<br>Thanks,<br>Odalric<br><br><br><div class=3D"gmail_quote">2010/3/4 Odalr=
ic-Ambrym Maillard <span dir=3D"ltr">&lt;<a href=3D"mailto:odalricambrym.ma=
illard@gmail.com">odalricambrym.maillard@gmail.com</a>&gt;</span><br><block=
quote class=3D"gmail_quote" style=3D"border-left: 1px solid rgb(204, 204, 2=
04); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Thanks, I was not aware of this relation between Bigarrays and C. <br>I wil=
l try to use this and tell you of it works as I want.<br><br>Odalric<br><br=
><div class=3D"gmail_quote">2010/3/4 Paolo Donadeo <span dir=3D"ltr">&lt;<a=
 href=3D"mailto:p.donadeo@gmail.com" target=3D"_blank">p.donadeo@gmail.com<=
/a>&gt;</span><div>
<div></div><div class=3D"h5"><br>
<blockquote class=3D"gmail_quote" style=3D"border-left: 1px solid rgb(204, =
204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">Did you consider =
using the bigarray library?<br>
<br>
<a href=3D"http://caml.inria.fr/pub/docs/manual-ocaml/manual043.html" targe=
t=3D"_blank">http://caml.inria.fr/pub/docs/manual-ocaml/manual043.html</a><=
br>
<br>
<br>
--<br>
Paolo<br>
<br>
_______________________________________________<br>
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=3D"_blank">http://yquem.inria.fr/cgi-bin/mailman/listinfo/caml-list</a><br=
>
Archives: <a href=3D"http://caml.inria.fr" target=3D"_blank">http://caml.in=
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</blockquote></div></div></div><br><br clear=3D"all"></blockquote></div><br=
>

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