👤
Home Man
Search
Today's Posts
Register

Linux & Unix Commands - Search Man Pages
Man Page or Keyword Search:
Select Section of Man Page:
Select Man Page Repository:

CentOS 7.0 - man page for dsgesv (centos section 3)

dsgesv.f(3)				      LAPACK				      dsgesv.f(3)

NAME
       dsgesv.f -

SYNOPSIS
   Functions/Subroutines
       subroutine dsgesv (N, NRHS, A, LDA, IPIV, B, LDB, X, LDX, WORK, SWORK, ITER, INFO)
	    DSGESV computes the solution to system of linear equations A * X = B for GE matrices
	   (mixed precision with iterative refinement)

Function/Subroutine Documentation
   subroutine dsgesv (integerN, integerNRHS, double precision, dimension( lda, * )A, integerLDA,
       integer, dimension( * )IPIV, double precision, dimension( ldb, * )B, integerLDB, double
       precision, dimension( ldx, * )X, integerLDX, double precision, dimension( n, * )WORK,
       real, dimension( * )SWORK, integerITER, integerINFO)
	DSGESV computes the solution to system of linear equations A * X = B for GE matrices
       (mixed precision with iterative refinement)

       Purpose:

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

	    DSGESV first attempts to factorize the matrix in SINGLE PRECISION
	    and use this factorization within an iterative refinement procedure
	    to produce a solution with DOUBLE PRECISION normwise backward error
	    quality (see below). If the approach fails the method switches to a
	    DOUBLE PRECISION factorization and solve.

	    The iterative refinement is not going to be a winning strategy if
	    the ratio SINGLE PRECISION performance over DOUBLE PRECISION
	    performance is too small. A reasonable strategy should take the
	    number of right-hand sides and the size of the matrix into account.
	    This might be done with a call to ILAENV in the future. Up to now, we
	    always try iterative refinement.

	    The iterative refinement process is stopped if
		ITER > ITERMAX
	    or for all the RHS we have:
		RNRM < SQRT(N)*XNRM*ANRM*EPS*BWDMAX
	    where
		o ITER is the number of the current iteration in the iterative
		  refinement process
		o RNRM is the infinity-norm of the residual
		o XNRM is the infinity-norm of the solution
		o ANRM is the infinity-operator-norm of the matrix A
		o EPS is the machine epsilon returned by DLAMCH('Epsilon')
	    The value ITERMAX and BWDMAX are fixed to 30 and 1.0D+00
	    respectively.

       Parameters:
	   N

		     N is INTEGER
		     The number of linear equations, i.e., 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 DOUBLE PRECISION array,
		     dimension (LDA,N)
		     On entry, the N-by-N coefficient matrix A.
		     On exit, if iterative refinement has been successfully used
		     (INFO.EQ.0 and ITER.GE.0, see description below), then A is
		     unchanged, if double precision factorization has been used
		     (INFO.EQ.0 and ITER.LT.0, see description below), then the
		     array A contains the factors L and U from the factorization
		     A = P*L*U; the unit diagonal elements of L are not stored.

	   LDA

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

	   IPIV

		     IPIV is INTEGER array, dimension (N)
		     The pivot indices that define the permutation matrix P;
		     row i of the matrix was interchanged with row IPIV(i).
		     Corresponds either to the single precision factorization
		     (if INFO.EQ.0 and ITER.GE.0) or the double precision
		     factorization (if INFO.EQ.0 and ITER.LT.0).

	   B

		     B is DOUBLE PRECISION array, dimension (LDB,NRHS)
		     The N-by-NRHS right hand side matrix B.

	   LDB

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

	   X

		     X is DOUBLE PRECISION array, dimension (LDX,NRHS)
		     If INFO = 0, the N-by-NRHS solution matrix X.

	   LDX

		     LDX is INTEGER
		     The leading dimension of the array X.  LDX >= max(1,N).

	   WORK

		     WORK is DOUBLE PRECISION array, dimension (N,NRHS)
		     This array is used to hold the residual vectors.

	   SWORK

		     SWORK is REAL array, dimension (N*(N+NRHS))
		     This array is used to use the single precision matrix and the
		     right-hand sides or solutions in single precision.

	   ITER

		     ITER is INTEGER
		     < 0: iterative refinement has failed, double precision
			  factorization has been performed
			  -1 : the routine fell back to full precision for
			       implementation- or machine-specific reasons
			  -2 : narrowing the precision induced an overflow,
			       the routine fell back to full precision
			  -3 : failure of SGETRF
			  -31: stop the iterative refinement after the 30th
			       iterations
		     > 0: iterative refinement has been sucessfully used.
			  Returns the number of iterations

	   INFO

		     INFO is INTEGER
		     = 0:  successful exit
		     < 0:  if INFO = -i, the i-th argument had an illegal value
		     > 0:  if INFO = i, U(i,i) computed in DOUBLE PRECISION is
			   exactly zero.  The factorization has been completed,
			   but the factor U is exactly singular, so the solution
			   could not be computed.

       Author:
	   Univ. of Tennessee

	   Univ. of California Berkeley

	   Univ. of Colorado Denver

	   NAG Ltd.

       Date:
	   November 2011

       Definition at line 195 of file dsgesv.f.

Author
       Generated automatically by Doxygen for LAPACK from the source code.

Version 3.4.2				 Tue Sep 25 2012			      dsgesv.f(3)


All times are GMT -4. The time now is 05:16 AM.

Unix & Linux Forums Content Copyrightę1993-2018. All Rights Reserved.
×
UNIX.COM Login
Username:
Password:  
Show Password