p?getf2

Developer Reference for Intel® oneAPI Math Kernel Library for Fortran

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ID 766686

Date 3/31/2023

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p?getf2

Computes an LU factorization of a general matrix, using partial pivoting with row interchanges (local blocked algorithm).

Syntax

call psgetf2(m, n, a, ia, ja, desca, ipiv, info)

call pdgetf2(m, n, a, ia, ja, desca, ipiv, info)

call pcgetf2(m, n, a, ia, ja, desca, ipiv, info)

call pzgetf2(m, n, a, ia, ja, desca, ipiv, info)

Description

The p?getf2routine computes an LU factorization of a general m-by-n distributed matrix sub(A) = A(ia:ia+m-1, ja:ja+n-1) using partial pivoting with row interchanges.

The factorization has the form sub(A) = P * L* U, where P is a permutation matrix, L is lower triangular with unit diagonal elements (lower trapezoidal if m>n), and U is upper triangular (upper trapezoidal if m < n). This is the right-looking Parallel Level 2 BLAS version of the algorithm.

Product and Performance Information
Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex. Notice revision #20201201

Product and Performance Information

Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.

Notice revision #20201201

Input Parameters

m

(global) INTEGER.

The number of rows in the distributed matrix sub(A). (m≥0).

n

(global) INTEGER. The number of columns in the distributed matrix sub(A). (nb_a - mod(ja-1, nb_a)≥n≥0).

a

(local).

REAL for psgetf2

DOUBLE PRECISION for pdgetf2

COMPLEX for pcgetf2

COMPLEX*16 for pzgetf2.

Pointer into the local memory to an array of size (lld_a, LOC_c(ja+n-1)).

On entry, this array contains the local pieces of the m-by-n distributed matrix sub(A).

ia, ja

(global) INTEGER. The row and column indices in the global matrix A indicating the first row and the first column of the matrix sub(A), respectively.

desca

(global and local) INTEGER array of size dlen_. The array descriptor for the distributed matrix A.

Output Parameters

ipiv

(local) INTEGER.

Array of size(LOCr(m_a) + mb_a). This array contains the pivoting information. ipiv(i) -> The global row that local row i was swapped with. This array is tied to the distributed matrix A.

info

(local). INTEGER.

If info = 0: successful exit.

If info < 0:

if the i-th argument is an array and the j-th entry had an illegal value, then info = -(i*100+j),
if the i-th argument is a scalar and had an illegal value, then info = - i.

If info > 0: If info = k, the matrix element U(ia+k-1, ja+k-1) is exactly zero. The factorization has been completed, but the factor U is exactly singular, and division by zero will occur if it is used to solve a system of equations.

Parent topic: ScaLAPACK Auxiliary Routines

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