Problem on TAUCS of a Novice

[Kye Wong]

Hi all:

I'm a novice on taucs and would like to solve the linear equations
using taucs,but I've got some problems on understanding the manual of
taucs 2.2

1 what does the colptr and rowind mean in taucs_ccs_matrix?
for example, a matrix
3,1,0
2,0,4
5,4.0
how to store it in taucs_ccs_matrix structure pls?

2 on solving the linear equation Ax=b
if A is an m*n matrix (m>n) and i want a least-square solution, which
"option" in taucs_linsolve should I use?

3 I've read some discussions on the bugs of taucs on the factorization
and solving of the above mentioned problem, so does it work if I
change "int opt_factor = 1" into " int opt_factor = 0"
and recompile taucs? or must I use the complex low level functions?

Thank you very much for your kindly instructions!

[Mark Hoemmen]

On Mon, Dec 14, 2009 at 07:44, Kye Wong <wang...@gmail.com> wrote:
> 1 what does the  colptr and rowind mean in  taucs_ccs_matrix?
> for example, a matrix
> 3,1,0
> 2,0,4
> 5,4.0
> how to store it in taucs_ccs_matrix structure pls?

http://www.netlib.org/linalg/html_templates/node92.html#SECTION00931200000000000000

Note carefully the differences in indexing between Fortran and C.

mfh

[You Li]

Kye Wong wrote:
> Hi all:
>
> I'm a novice on taucs and would like to solve the linear equations
> using taucs,but I've got some problems on understanding the manual of
> taucs 2.2
>
> 1 what does the colptr and rowind mean in taucs_ccs_matrix?
> for example, a matrix
> 3,1,0
> 2,0,4
> 5,4.0
> how to store it in taucs_ccs_matrix structure pls?
>

I believe this link will explain everything:
http://netlib.org/linalg/html_templates/node92.html

> 2 on solving the linear equation Ax=b
> if A is an m*n matrix (m>n) and i want a least-square solution, which
> "option" in taucs_linsolve should I use?
>

This is a over-determined system. So far as I know, Taucs can't solve
over-determined system. But If this is a full-rank matrix, you can try
normal equations method to transform you A into A^T *A.

> 3 I've read some discussions on the bugs of taucs on the factorization
> and solving of the above mentioned problem, so does it work if I
> change "int opt_factor = 1" into " int opt_factor = 0"
> and recompile taucs? or must I use the complex low level functions?
>
> Thank you very much for your kindly instructions!
>

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>

[Alejandro A. Ortiz Bernardin]

>> 2 on solving the linear equation Ax=b
>> if A is an m*n matrix (m>n) and i want a least-square solution, which
>> "option" in taucs_linsolve should I use?

I don't know the origin of your problem, but you should be able to transform
your problem into one of square matrix where you can use TAUCS. Look at this
paper:

http://www.nealen.net/projects/mls/asapmls.pdf

[Kye Wong]

Thank you guys!

The first two problems is clear by now!

But what about the third problem? Does taucs really have bugs for separating the factorization and solving operations? Must I use the low-level functions or is there any other easier way of doing these operations just using "taucs_linsolve" pls?

Thank you again for your kindly help!

--

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--
Kye Wong

[You Li]

There were bugs about using iterative solver, but I didn't have problem
using direct solver.

> <mailto:matrixpr...@googlegroups.com>.

> To unsubscribe from this group, send email to
> matrixprogramm...@googlegroups.com

> <mailto:matrixprogramming%2Bunsu...@googlegroups.com>.

[Kye Wong]

Thanks!

Then when I try the taucs like follows, "TAUCS_ERROR_NOMEM" always
come out. could you pls give me some idea on that?
Thank you!


double value[6];
int colptr[4];
int rowind[6];
double RHS[3];

// create CCS matrix structure using vector class
value[0]=1;
value[1]=2;
value[2]=3;
value[3]=2;
value[4]=4;
value[5]=3;

colptr[0]=0;
colptr[1]=3;
colptr[2]=5;
colptr[3]=6;

rowind[0]=0;
rowind[1]=0;
rowind[2]=0;
rowind[3]=1;
rowind[4]=1;
rowind[5]=2;

// create right-hand size vector object
RHS[0] = 10;
RHS[1] = 2;
RHS[2] = 3;

// resize vectors.
int dim = 3;

// create TAUCS matrix from vector objects an, jn and ia
taucs_ccs_matrix A; // a matrix to solve Ax=b in CCS format
A.n = dim;
A.m = dim;
A.flags = (TAUCS_DOUBLE | TAUCS_SYMMETRIC);
A.colptr = colptr;
A.rowind = rowind;
A.values.d = value;

// allocate TAUCS solution vector
double x[3];

// solve the linear system
void* F = NULL;
char* options[] = {"taucs.factor.LU=true", NULL};
void* opt_arg[] = { NULL };

int i = taucs_linsolve(&A, &F, 1, x, RHS, options, opt_arg);

if (i != TAUCS_SUCCESS)
{
cout << "Solution error." << endl;
if (i==TAUCS_ERROR)
cout << "Generic error." << endl;

if (i==TAUCS_ERROR_NOMEM)
cout << "NOMEM error." << endl;

if (i==TAUCS_ERROR_BADARGS)
cout << "BADARGS error." << endl;

if (i==TAUCS_ERROR_MAXDEPTH)
cout << "MAXDEPTH error." << endl;

if (i==TAUCS_ERROR_INDEFINITE)
cout << "NOT POSITIVE DEFINITE error." << endl;
}
else
{
cout << "Solution success." << endl;

for (unsigned j = 0; j < 4; j++)
cout << x[j] << endl;
}

// deallocate the factorization
taucs_linsolve(NULL, &F, 0, NULL, NULL, NULL, NULL);