NAME

dtrsv - solve one of the systems of equations   A∗x = b or A’∗x = b

SYNOPSIS

SUBROUTINE DTRSV
( UPLO, TRANS, DIAG, N, A, LDA, X, INCX )

void dtrsv(char uplo, char trans, char diag, long int n,
double ∗da, long int lda, double ∗dx, long int incx)

INTEGER INCX, LDA, N

CHARACTER∗1 DIAG, TRANS, UPLO

DOUBLE PRECISION A( LDA, ∗ ), X( ∗ )

PURPOSE

DTRSV  solves one of the systems of equations A∗x = b or A’∗x = b where b and x are n element vectors and A is an n by n unit, or non-unit, upper or lower triangular matrix. 
 
No test for singularity or near-singularity is included in this routine. Such tests must be performed before calling this routine.
 

PARAMETERS

UPLO   - CHARACTER∗1. 
On entry, UPLO specifies whether the matrix is an upper or lower triangular matrix as follows:
 
UPLO = ’U’ or ’u’   A is an upper triangular matrix.
 
UPLO = ’L’ or ’l’   A is a lower triangular matrix.
 
Unchanged on exit.

TRANS  - CHARACTER∗1. 
On entry, TRANS specifies the equations to be solved as follows:
 
TRANS = ’N’ or ’n’   A∗x = b.
 
TRANS = ’T’ or ’t’   A’∗x = b.
 
TRANS = ’C’ or ’c’   A’∗x = b.
 
Unchanged on exit.

DIAG   - CHARACTER∗1. 
On entry, DIAG specifies whether or not A is unit triangular as follows:
 
DIAG = ’U’ or ’u’   A is assumed to be unit triangular.
 
DIAG = ’N’ or ’n’   A is not assumed to be unit triangular.
 
Unchanged on exit.

N      - INTEGER. 
On entry, N specifies the order of the matrix A. N must be at least zero. Unchanged on exit.

A      - DOUBLE PRECISION array of DIMENSION ( LDA, n ). 
Before entry with  UPLO = ’U’ or ’u’, the leading n by n upper triangular part of the array A must contain the upper triangular matrix and the strictly lower triangular part of A is not referenced. Before entry with UPLO = ’L’ or ’l’, the leading n by n lower triangular part of the array A must contain the lower triangular matrix and the strictly upper triangular part of A is not referenced. Note that when  DIAG = ’U’ or ’u’, the diagonal elements of A are not referenced either, but are assumed to be unity. Unchanged on exit.

LDA    - INTEGER. 
On entry, LDA specifies the first dimension of A as declared in the calling (sub) program. LDA must be at least max( 1, n ). Unchanged on exit.

X      - DOUBLE PRECISION array of dimension at least
( 1 + ( n - 1 )∗abs( INCX ) ). Before entry, the incremented array X must contain the n element right-hand side vector b. On exit, X is overwritten with the solution vector x.

INCX   - INTEGER. 
On entry, INCX specifies the increment for the elements of X. INCX must not be zero. Unchanged on exit.

Sun, Inc.  —  Last change: 20 Sep 1996