Re: [Lapackpp-devel] Memory Allocation

[kevin c. <kev...@gm...>]

Hi,

   The code that I am using is below.  The aim is to define a matrix,
V, of size D_rows x D_rows and fill a diagonal band of width ~ M with
values and then the rest with zeros.  It is symmetric, so I calculate
the diagonal and super-diagonal elements and then copy these into the
correct sub-diagonal elements.

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<iostream>
#include<math.h>
#include<lapackpp.h>=20

int main()
{
...
      int N =3D numberOfLines;        //The value of numberOfLines is
determined earlier
                                                //in the code by
counting the number of lines in a
                                                //data file.
      int M =3D expDegree;             //M is determined earlier in the
file by user input
      int D_rows =3D N-M-1;
      LaGenMatDouble V(D_rows,D_rows);
...

=09for(i=3D0;i<D_rows;i++)
=09{
=09=09sum =3D 0.0;
=09=09for(k=3D0;k<M;k++)
=09=09{
=09=09=09sum +=3D p(k,0)*p(k,0)*y(i-k+M-1,1);
=09=09}
=09=09V(i,i) =3D y(i+M,1) + sum;
=09=09if(!V(i,i))
=09=09{
=09=09=09V(i,i) =3D 1;
=09=09}
=09=09for(j=3Di+1;(j-i)<V_sd;j++)
=09=09{
=09=09=09sum =3D 0.0;
=09=09=09for(k=3D0;k<M-j;k++)
=09=09=09{
=09=09=09=09sum +=3D p(k,0)*p(k+j-i,0)*y(i+M-k-1,1);
=09=09=09}
=09=09=09V(i,j) =3D -p(j-i-1,0)*y(i+M,1) + sum;
=09=09=09if(!V(i,i))
=09=09=09{
=09=09=09=09V(i,i) =3D 1;
=09=09=09}
=09=09}
=09=09for(j=3Di+V_sd;j<D_rows;j++)
=09=09{
=09=09=09V(i,j) =3D 0.0;
=09=09}
=09}
=09for(i=3D0;i<D_rows;i++)
=09{
=09=09for(j=3D0;j<i;j++)
=09=09{
=09=09=09V(i,j) =3D V(j,i);
=09=09}
=09}
...
       return 0;
}


This is the offending section of code.  It will work fine until I get
to N ~ 128 and then gives a segmentation fault.  I can make the fault
go away again by choosing a sufficiently large M (which reduces the
size of D_rows), but this is not really practical, as M is a
meaningful parameter in my model!

  Cheers,
          Kevin


On 16/09/05, Christian Stimming <sti...@tu...> wrote:
> Hi Kevin,
>=20
> can you provide some example code that demonstrates the error?
> Allocation itself usually is not a problem, even for much larger
> matrices (can be verified by ./matrix/testing/tgd 200 200).
>=20
> However, it is true that lapackpp unfortunately doesn't check for
> successful allocation of a new matrix. I'll add this in CVS soon.
>=20
> Regards,
>=20
> Christian
>=20
> kevin channon schrieb:
> > Hi,
> >
> >     I have used lapack++ to allocate memory for a 128x128 element
> > matrix (LaGenMatDouble), which works fine.  When I try to allocate
> > values to the elements I get a segmentation fault.  As I understand
> > it, this means that my program is trying to access memory that has not
> > been allocated to it.  The error goes away if I use a smaller matrix
> > (113x113, for example), so I think that the code works, it just runs
> > out of memory.  I was wondering if this is due to the memory being
> > allocated on the stack instead of the heap, thus not giving much room
> > for large arrays.  If so, how can I get the memory allocated to the
> > heap instead?  If not, does anyone know what the problem could be?
>