psdtsv(3) [debian man page]

PSDTSV(l)						   LAPACK routine (version 1.5) 						 PSDTSV(l)

NAME

       PSDTSV - solve a system of linear equations   A(1:N, JA:JA+N-1) * X = B(IB:IB+N-1, 1:NRHS)

SYNOPSIS

       SUBROUTINE PSDTSV( N, NRHS, DL, D, DU, JA, DESCA, B, IB, DESCB, WORK, LWORK, INFO )

	   INTEGER	  IB, INFO, JA, LWORK, N, NRHS

	   INTEGER	  DESCA( * ), DESCB( * )

	   REAL 	  B( * ), D( * ), DL( * ), DU( * ), WORK( * )

PURPOSE

       PSDTSV solves a system of linear equations

       where A(1:N, JA:JA+N-1) is an N-by-N real
       tridiagonal diagonally dominant-like distributed
       matrix.

       Gaussian elimination without pivoting
       is used to factor a reordering
       of the matrix into L U.

       See PSDTTRF and PSDTTRS for details.

LAPACK version 1.5						    12 May 1997 							 PSDTSV(l)

DSYSV(l)								 )								  DSYSV(l)

NAME

       DSYSV - compute the solution to a real system of linear equations A * X = B,

SYNOPSIS

       SUBROUTINE DSYSV( UPLO, N, NRHS, A, LDA, IPIV, B, LDB, WORK, LWORK, INFO )

	   CHARACTER	 UPLO

	   INTEGER	 INFO, LDA, LDB, LWORK, N, NRHS

	   INTEGER	 IPIV( * )

	   DOUBLE	 PRECISION A( LDA, * ), B( LDB, * ), WORK( * )

PURPOSE

       DSYSV computes the solution to a real system of linear equations A * X = B, where A is an N-by-N symmetric matrix and X and B are N-by-NRHS
       matrices.

       The diagonal pivoting method is used to factor A as
	  A = U * D * U**T,  if UPLO = 'U', or
	  A = L * D * L**T,  if UPLO = 'L',
       where U (or L) is a product of permutation and unit upper (lower) triangular matrices, and D is symmetric and block  diagonal  with  1-by-1
       and 2-by-2 diagonal blocks.  The factored form of A is then used to solve the system of equations A * X = B.

ARGUMENTS

       UPLO    (input) CHARACTER*1
	       = 'U':  Upper triangle of A is stored;
	       = 'L':  Lower triangle of A is stored.

       N       (input) INTEGER
	       The number of linear equations, i.e., 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/output) DOUBLE PRECISION array, dimension (LDA,N)
	       On  entry, the symmetric matrix A.  If UPLO = 'U', the leading N-by-N upper triangular part of A contains the upper triangular part
	       of the matrix A, and the strictly lower triangular part of A is not referenced.	If UPLO = 'L', the leading N-by-N lower triangular
	       part of A contains the lower triangular part of the matrix A, and the strictly upper triangular part of A is not referenced.

	       On  exit,  if INFO = 0, the block diagonal matrix D and the multipliers used to obtain the factor U or L from the factorization A =
	       U*D*U**T or A = L*D*L**T as computed by DSYTRF.

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

       IPIV    (output) INTEGER array, dimension (N)
	       Details of the interchanges and the block structure of D, as determined by DSYTRF.  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 UPLO = 'U' and IPIV(k) = IPIV(k-1) < 0, then rows and columns
	       k-1 and -IPIV(k) were interchanged and D(k-1:k,k-1:k) is a 2-by-2 diagonal block.  If UPLO = 'L' and IPIV(k) = IPIV(k+1) < 0,  then
	       rows and columns k+1 and -IPIV(k) were interchanged and D(k:k+1,k:k+1) is a 2-by-2 diagonal block.

       B       (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS)
	       On entry, the N-by-NRHS right hand side matrix B.  On exit, if INFO = 0, the N-by-NRHS solution matrix X.

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

       WORK    (workspace/output) DOUBLE PRECISION array, dimension (LWORK)
	       On exit, if INFO = 0, WORK(1) returns the optimal LWORK.

       LWORK   (input) INTEGER
	       The length of WORK.  LWORK >= 1, and for best performance LWORK >= N*NB, where NB is the optimal blocksize for DSYTRF.

	       If  LWORK  =  -1,  then	a workspace query is assumed; the routine only calculates the optimal size of the WORK array, returns this
	       value as the first entry of the WORK array, and no error message related to LWORK is issued by XERBLA.

       INFO    (output) INTEGER
	       = 0: successful exit
	       < 0: if INFO = -i, the i-th argument had an illegal value
	       > 0: if INFO = i, D(i,i) is exactly zero.  The factorization has been completed, but the block diagonal matrix D is exactly  singu-
	       lar, so the solution could not be computed.

LAPACK version 3.0						   15 June 2000 							  DSYSV(l)