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Technical Reference: Base Operating System and Extensions, Volume 2
STRSV, DTRSV, CTRSV, or ZTRSV Subroutine
Purpose
Solves system of equations.
Library
BLAS Library (libblas.a)
FORTRAN Syntax
SUBROUTINE STRSV(UPLO, TRANS, DIAG,
N, A, LDA, X, INCX)
INTEGER INCX, LDA, N
CHARACTER*1 DIAG, TRANS, UPLO
REAL A(LDA,*), X(*)
SUBROUTINE DTRSV(UPLO, TRANS, DIAG,
N, A, LDA, X, INCX)
INTEGER INCX,LDA,N
CHARACTER*1 DIAG,TRANS,UPLO
DOUBLE PRECISION A(LDA,*), X(*)
SUBROUTINE CTRSV(UPLO, TRANS, DIAG,
N, A, LDA, X, INCX)
INTEGER INCX,LDA,N
CHARACTER*1 DIAG,TRANS,UPLO
COMPLEX A(LDA,*), X(*)
SUBROUTINE ZTRSV(UPLO, TRANS, DIAG,
N, A, LDA, X, INCX)
INTEGER INCX,LDA,N
CHARACTER*1 DIAG,TRANS,UPLO
COMPLEX*16 A(LDA,*), X(*)
Description
The STRSV, DTRSV, CTRSV, or ZTRSV subroutine
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 |
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 |
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 |
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 |
On entry, N specifies the order of the matrix A; N must be at least 0; unchanged
on exit. |
A |
An array of dimension ( LDA, N ); on 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. On 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. When DIAG = 'U' or 'u', the diagonal elements
of A are not referenced, but are assumed to be unity;
unchanged on exit. |
LDA |
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 |
A vector of dimension at least (1 + (N-1)
* abs(INCX) ); on 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 |
On entry, INCX specifies the increment for
the elements of X; INCX must
not be 0; unchanged on exit. |
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