topic Re: dpotri problem when calling from C in Intel® oneAPI Math Kernel Library

dpotri problem when calling from C

danesh_d — Tue, 18 Nov 2008 22:31:48 GMT

Hi,

I want to calculate inversion of a symmetric matrix using Cholesky factorization in C using "dpotri" MKL's LAPACK function. I wrote this code:

int info=0;
int param1=n*n;
int param2=n;
char* uplo="U";
dpotri(uplo, &param1, M, &param2, &info);

where "M" is a "nxn" symmetric matrix. The is compiled successfully but when I run the pogram, it says that parameter 4 (LDA which is defined "n" here) is incorrect. Should't it be "n" for a "nxn" matrix? Also, should I call "dpotrf" before "dpotri"?

Thanks for your help,

Re: dpotri problem when calling from C

TimP — Tue, 18 Nov 2008 23:10:40 GMT

Quoting - danesh_d

int info=0;
int param1=n*n;
int param2=n;
char* uplo="U";
dpotri(uplo, &param1, M, &param2, &info);

Should it be param1=n ? The matrix has to be dimensionedby the square of that value, which may not exceed param2.

It does require execution of potrf first.

http://www.intel.com/software/products/mkl/docs/WebHelp/lle/functn_potri.html

Re: dpotri problem when calling from C

danesh_d — Tue, 18 Nov 2008 23:33:20 GMT

Quoting - tim18

Should it be param1=n ? The matrix has to be dimensionedby the square of that value, which may not exceed param2.

It does require execution of potrf first.

http://www.intel.com/software/products/mkl/docs/WebHelp/lle/functn_potri.html

I think param1 is set correctly which is "n^2" for an "nxn" matrix which is order of that matrix. param2 is the problem which is "LDA" and should be "LDA>=max(1, param1)". Am I right? I don't know what "LDA" is. It is defined as "first dimension of matrix". I set param1=n and param2=n*n and got "segmentation fault" error. Same error for param1=param2=n*n.

Re: dpotri problem when calling from C

Michael_C_Intel4 — Mon, 24 Nov 2008 14:31:53 GMT

Hello,

param1 should definitely be set to the linear size of the matrix.

LDA is "a leading dimension of A", it could be referred to as a stride. If 2-d array is continuous in memory, the stride is equal to the first dimension of the matrix (in case of 2-d array in C language it would be the last dimension).

In your particular case param1=param2=n should be set.

Michael.