## Data error in triangular factorization

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**1**of**1**### Data error in triangular factorization

Seems like LU factorization works only for full rank (row or column rank) matrices...

Is this a limitation of the beta, or is this an unimplemented feature?

Below is the example code that I use to run... 32Bit FC10, GTX295 Cuda 2.3

=============================================================

// This example is meant to show a typical program flow when using CULA.

int main(int argc, char** argv)

{

#ifdef NDEBUG

int M = 3;

#else

int M = 3;

#endif

int N = M;

int LWORK = 0;

culaStatus status;

float* A = NULL;

int* TAU = NULL;

A = (float*)malloc(M*N*sizeof(float));

TAU = (int*)malloc((M<N?M:N)*sizeof(int));

uint i,j;

for(i=0;i<M;i++)

for(j=0;j<N;j++)

{

*(A+j*M+i) = (float)(i+j+((int)rand())%10);

printf("%f\t",*(A+j*M+i));

}

if(!A || !TAU)

{

free(A);

free(TAU);

return EXIT_FAILURE;

}

printf("Initializing CULA\n");

status = culaInitialize();

checkStatus(status);

memset(A, 1, M*N*sizeof(float));

printf("Calling SGETRF\n");

status = culaSgetrf(M, N, A, M, TAU);

checkStatus(status);

culaShutdown();

free(A);

free(TAU);

return EXIT_SUCCESS;

}

Is this a limitation of the beta, or is this an unimplemented feature?

Below is the example code that I use to run... 32Bit FC10, GTX295 Cuda 2.3

=============================================================

// This example is meant to show a typical program flow when using CULA.

int main(int argc, char** argv)

{

#ifdef NDEBUG

int M = 3;

#else

int M = 3;

#endif

int N = M;

int LWORK = 0;

culaStatus status;

float* A = NULL;

int* TAU = NULL;

A = (float*)malloc(M*N*sizeof(float));

TAU = (int*)malloc((M<N?M:N)*sizeof(int));

uint i,j;

for(i=0;i<M;i++)

for(j=0;j<N;j++)

{

*(A+j*M+i) = (float)(i+j+((int)rand())%10);

printf("%f\t",*(A+j*M+i));

}

if(!A || !TAU)

{

free(A);

free(TAU);

return EXIT_FAILURE;

}

printf("Initializing CULA\n");

status = culaInitialize();

checkStatus(status);

memset(A, 1, M*N*sizeof(float));

printf("Calling SGETRF\n");

status = culaSgetrf(M, N, A, M, TAU);

checkStatus(status);

culaShutdown();

free(A);

free(TAU);

return EXIT_SUCCESS;

}

Senior Developer, AccelerEyes

PhD Student, Dept. of ECE,

UC Santa Barbara

- jrk1982
**Posts:**26**Joined:**Thu Aug 13, 2009 8:48 pm

### Re:Data error in triangular factorization

The LAPACK-style LU factorization doesn't work on rank deficient matrices; it considers them singular and rather than diving by zero returns a code to indicate singularity. Receiving a culaDataError is equivalent to a "info" code > 0 in other implementations. In this respect, we should be providing identical functionality.

For more information, please see: http://www.intel.com/software/products/ ... getrf.html

It's worth noting that getrf() is valid on non-square matrices (both over- and under-determined) as long as they're still full rank.

I hope this answers your question. If I have misunderstood, can you please reply back with more information.

Thanks,

John

For more information, please see: http://www.intel.com/software/products/ ... getrf.html

It's worth noting that getrf() is valid on non-square matrices (both over- and under-determined) as long as they're still full rank.

I hope this answers your question. If I have misunderstood, can you please reply back with more information.

Thanks,

John

- john
- Administrator
**Posts:**587**Joined:**Thu Jul 23, 2009 2:31 pm

### Re:Data error in triangular factorization

Sure. Thanks for the clarification.

But I still get Data Error with the code snipped I had attached. The matrix input is full rank I believe...

Also, MATLAB behaves differently(well) for singular matrix inputs?!

Thanks for looking into this matter!

But I still get Data Error with the code snipped I had attached. The matrix input is full rank I believe...

Also, MATLAB behaves differently(well) for singular matrix inputs?!

Thanks for looking into this matter!

Senior Developer, AccelerEyes

PhD Student, Dept. of ECE,

UC Santa Barbara

- jrk1982
**Posts:**26**Joined:**Thu Aug 13, 2009 8:48 pm

### Re:Data error in triangular factorization

I see a quick error in your code:

memset(A, 1, M*N*sizeof(float));

This line sets your entire matrix to 2.36942e-38 for every value, which is rank deficient.

memset(A, 1, M*N*sizeof(float));

This line sets your entire matrix to 2.36942e-38 for every value, which is rank deficient.

- john
- Administrator
**Posts:**587**Joined:**Thu Jul 23, 2009 2:31 pm

### Re:Data error in triangular factorization

Oops. Good catch. I ought to have to have removed that :) Thanks.

Senior Developer, AccelerEyes

PhD Student, Dept. of ECE,

UC Santa Barbara

- jrk1982
**Posts:**26**Joined:**Thu Aug 13, 2009 8:48 pm

### Re:Data error in triangular factorization

Thanks. That worked for the LU factors. However, 1 last issue which I think is genuine.

The permutation vector returned does not seem right... I get [3 3 3] for input, [3 7 9; 6 5 8; 8 5 13]. Matlab returns [3 1 2]...

The permutation vector returned does not seem right... I get [3 3 3] for input, [3 7 9; 6 5 8; 8 5 13]. Matlab returns [3 1 2]...

Senior Developer, AccelerEyes

PhD Student, Dept. of ECE,

UC Santa Barbara

- jrk1982
**Posts:**26**Joined:**Thu Aug 13, 2009 8:48 pm

### Re:Data error in triangular factorization

That's just a notational difference. Matlab's vector is meant to be evaluated in parallel (ie A(p,: )) and LAPACK's is procedural (apply this swap, THEN do this swap, THEN do this one, etc.) In this case they're equivalent.

- john
- Administrator
**Posts:**587**Joined:**Thu Jul 23, 2009 2:31 pm

### Re:Data error in triangular factorization

Cool. Thanks!

Senior Developer, AccelerEyes

PhD Student, Dept. of ECE,

UC Santa Barbara

- jrk1982
**Posts:**26**Joined:**Thu Aug 13, 2009 8:48 pm

### Re:Data error in triangular factorization

Hi,

I run this code (I removed the memset), but I cannot get the permutation vector as [3 3 3]. TAU vector here returns weird digits as 4.204e-045#DEN, any idea?!

Thanks a lot

I run this code (I removed the memset), but I cannot get the permutation vector as [3 3 3]. TAU vector here returns weird digits as 4.204e-045#DEN, any idea?!

Thanks a lot

University of Alberta

- kolonel
**Posts:**14**Joined:**Mon Oct 26, 2009 9:18 pm**Location:**Canada

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