DTRTRS - solve a triangular system of the form A * X = B
or A**T * X = B,
SYNOPSIS
SUBROUTINE DTRTRS( UPLO, TRANS, DIAG, N, NRHS, A, LDA, B,
LDB, INFO )
CHARACTER DIAG, TRANS, UPLO
INTEGER INFO, LDA, LDB, N, NRHS
DOUBLE PRECISION A( LDA, * ), B( LDB, * )
PURPOSE
DTRTRS 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. A check is made to verify
that A is nonsingular.
ARGUMENTS
UPLO (input) CHARACTER*1
= 'U': A is upper triangular;
= 'L': A is lower triangular.
TRANS (input) 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 (input) CHARACTER*1
= 'N': A is non-unit triangular;
= 'U': A is unit triangular.
N (input) INTEGER
The order of the matrix A. N >= 0.
NRHS (input) INTEGER
The number of right hand sides, i.e., the number
of columns of the matrix B. NRHS >= 0.
A (input) DOUBLE PRECISION array, dimension (LDA,N)
The triangular matrix A. If UPLO = 'U', the lead
ing 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 refer
enced. If UPLO = 'L', the leading N-by-N lower
triangular part of the array A contains the lower
triangular matrix, and the strictly upper triangu
lar part of A is not referenced. If DIAG = 'U',
the diagonal elements of A are also not referenced
LDA (input) INTEGER
The leading dimension of the array A. LDA >=
max(1,N).
B (input/output) DOUBLE PRECISION array,
dimension (LDB,NRHS)
On entry, the right hand side matrix B. On exit,
if INFO = 0, the solution matrix X.
LDB (input) INTEGER
The leading dimension of the array B. LDB >=
max(1,N).
INFO (output) INTEGER
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an ille
gal value
> 0: if INFO = i, the i-th diagonal element of A
is zero, indicating that the matrix is singular
and the solutions X have not been computed.
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