SRC/strtrs.f(3) | Library Functions Manual | SRC/strtrs.f(3) |
NAME
SRC/strtrs.f
SYNOPSIS
Functions/Subroutines
subroutine strtrs (uplo, trans, diag, n, nrhs, a, lda, b,
ldb, info)
STRTRS
Function/Subroutine Documentation
subroutine strtrs (character uplo, character trans, character diag, integer n, integer nrhs, real, dimension( lda, * ) a, integer lda, real, dimension( ldb, * ) b, integer ldb, integer info)
STRTRS
Purpose:
!> !> STRTRS solves a triangular system of the form !> !> A * X = B or A**T * X = B, !> !> where A is a triangular matrix of order N, and B is an N-by-NRHS matrix. !> !> This subroutine verifies that A is nonsingular, but callers should note that only exact !> singularity is detected. It is conceivable for one or more diagonal elements of A to be !> subnormally tiny numbers without this subroutine signalling an error. !> !> If a possible loss of numerical precision due to near-singular matrices is a concern, the !> caller should verify that A is nonsingular within some tolerance before calling this subroutine. !>
Parameters
UPLO
!> UPLO is CHARACTER*1 !> = 'U': A is upper triangular; !> = 'L': A is lower triangular. !>
TRANS
!> TRANS is CHARACTER*1 !> Specifies the form of the system of equations: !> = 'N': A * X = B (No transpose) !> = 'T': A**T * X = B (Transpose) !> = 'C': A**H * X = B (Conjugate transpose = Transpose) !>
DIAG
!> DIAG is CHARACTER*1 !> = 'N': A is non-unit triangular; !> = 'U': A is unit triangular. !>
N
!> N is INTEGER !> The order of the matrix A. N >= 0. !>
NRHS
!> NRHS is INTEGER !> The number of right hand sides, i.e., the number of columns !> of the matrix B. NRHS >= 0. !>
A
!> A is REAL array, dimension (LDA,N) !> The triangular matrix A. If UPLO = 'U', the leading N-by-N !> upper triangular part of the array A contains the upper !> triangular matrix, and the strictly lower triangular part of !> A is not referenced. If UPLO = 'L', the leading N-by-N lower !> triangular part of the array A contains the lower triangular !> matrix, and the strictly upper triangular part of A is not !> referenced. If DIAG = 'U', the diagonal elements of A are !> also not referenced and are assumed to be 1. !>
LDA
!> LDA is INTEGER !> The leading dimension of the array A. LDA >= max(1,N). !>
B
!> B is REAL array, dimension (LDB,NRHS) !> On entry, the right hand side matrix B. !> On exit, if INFO = 0, the solution matrix X. !>
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 = -i, the i-th argument had an illegal value !> > 0: if INFO = i, the i-th diagonal element of A is exactly zero, !> indicating that the matrix is singular and the solutions !> X have not been computed. !>
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Definition at line 144 of file strtrs.f.
Author
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