TESTING/LIN/slavsy.f(3)

💅 NAME

TESTING/LIN/slavsy.f — okay so this is the TESTING/LIN/slavsy.f(3) page from the Library Functions Manual, and it's all about SLAVSY. Lowkey iconic Fortran subroutine behavior, fr fr. 🫶

✨ SYNOPSIS ✨

Functions/Subroutines

subroutine slavsy (uplo, trans, diag, n, nrhs, a, lda, ipiv, b, ldb,
           info)
           SLAVSY

🌸 Function/Subroutine Documentation 🌸

subroutine slavsy (character uplo, character trans, character diag, integer
       n, integer nrhs, real, dimension( lda, * ) a, integer lda, integer,
       dimension( * ) ipiv, real, dimension( ldb, * ) b, integer ldb, integer
       info)
       SLAVSY

🎯 Purpose

Okay bestie, here's the vibe: SLAVSY performs one of the matrix-vector operations

x := A*x  or  x := A'*x,

where x is an N element vector and A is one of the factors from the block U*D*U' or L*D*L' factorization computed by SSYTRF. 🦋

• If TRANS = 'N', multiplies by U or U * D (or L or L * D)
• If TRANS = 'T', multiplies by U' or D * U' (or L' or D * L')
• If TRANS = 'C', multiplies by U' or D * U' (or L' or D * L')

🧚 Parameters

UPLO

UPLO is CHARACTER*1. It specifies whether the factor stored in A is upper or lower triangular.

• = 'U': Upper triangular
• = 'L': Lower triangular

TRANS

TRANS is CHARACTER*1. It specifies the operation to be performed:

• = 'N': x := A*x
• = 'T': x := A'*x
• = 'C': x := A'*x

DIAG

DIAG is CHARACTER*1. It specifies whether or not the diagonal blocks are unit matrices. If the diagonal blocks are assumed to be unit, then A = U or A = L, otherwise A = U*D or A = L*D.

• = 'U': Diagonal blocks are assumed to be unit matrices.
• = 'N': Diagonal blocks are assumed to be non-unit matrices.

N

N is INTEGER. The number of rows and columns of the matrix A. N >= 0.

NRHS

NRHS is INTEGER. The number of right hand sides, i.e., the number of vectors x to be multiplied by A. NRHS >= 0.

A

A is REAL array, dimension (LDA,N). The block diagonal matrix D and the multipliers used to obtain the factor U or L as computed by SSYTRF. Stored as a 2-D triangular matrix.

LDA

LDA is INTEGER. The leading dimension of the array A. LDA >= max(1,N).

IPIV

IPIV is INTEGER array, dimension (N). Details of the interchanges and the block structure of D, as determined by SSYTRF.

If UPLO = 'U':

• If IPIV(k) > 0, then rows and columns k and IPIV(k) were interchanged and D(k,k) is a 1-by-1 diagonal block. (If IPIV( k ) = k, no interchange was done).
• If IPIV(k) = IPIV(k-1) < 0, then rows and columns k-1 and -IPIV(k) were interchanged, D(k-1:k,k-1:k) is a 2-by-2 diagonal block.

If UPLO = 'L':

• If IPIV(k) > 0, then rows and columns k and IPIV(k) were interchanged and D(k,k) is a 1-by-1 diagonal block. (If IPIV( k ) = k, no interchange was done).
• If IPIV(k) = IPIV(k+1) < 0, then rows and columns k+1 and -IPIV(k) were interchanged, D(k:k+1,k:k+1) is a 2-by-2 diagonal block.

B

B is REAL array, dimension (LDB,NRHS). On entry, B contains NRHS vectors of length N. On exit, B is overwritten with the product A * B. 💖

LDB

LDB is INTEGER. The leading dimension of the array B. LDB >= max(1,N).

INFO

INFO is INTEGER.

• = 0: successful exit
• < 0: if INFO = -k, the k-th argument had an illegal value

👑 Author

• Univ. of Tennessee
• Univ. of California Berkeley
• Univ. of Colorado Denver
• NAG Ltd.

Definition at line 153 of file slavsy.f.

🤖 Author

Generated automatically by Doxygen for LAPACK from the source code.

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okay that's the whole page, bestie — source/version: LAPACK Version 3.12.0, and the date: not printed in this copy, so I'm not inventing one. Page: TESTING/LIN/slavsy.f(3). now go slay those symmetric matrices 💅✨