LAPACK/ScaLAPACK Development

Can anyone help me ?
When I use this routine , I cann't get the right inverse of a matrix. If matrix is a uptriangular matrix ,the answer is right ,but when matrix is general, the answer is not correct.
How to use it ? How to set the ipiv .
Can anyone help me? Thank you!

Can anyone give me an example on how to use this routine?
Thankyou!

Before calling DGETRI you first need to call DGETRF.

In C, the calling sequence looks like :

Code: Select all

      dgetrf_( &n, &n, a, &lda, ipiv, &info );
      if (info==0)
           dgetri_( &n, a, &lda, ipiv, work, &lwork, &info );


DGETRF will perform the LU factorization of A and take care of ipiv for you.
This piece of code works for any nonsingular matrix.

Julien

PS: Your observation is correct. If you have a upper triangular matrix: there is no pivoting, the U factor is the matrix itself and the L factor is the identity. So basically you do not need DGETRF. DGETRF on A upper triangular returns A unchanged. (Regarding the pivot in IPIV, you are a bit more lucky....)

Julien:
Thank you very much. With your help , I have got the right answer.