dlasy2.f (3) Linux Manual Page

dlasy2.f –

Synopsis

Functions/Subroutines

subroutine dlasy2 (LTRANL, LTRANR, ISGN, N1, N2, TL, LDTL, TR, LDTR, B, LDB, SCALE, X, LDX, XNORM, INFO)
DLASY2 solves the Sylvester matrix equation where the matrices are of order 1 or 2.

Function/Subroutine Documentation

subroutine dlasy2 (logicalLTRANL, logicalLTRANR, integerISGN, integerN1, integerN2, double precision, dimension( ldtl, * )TL, integerLDTL, double precision, dimension( ldtr, * )TR, integerLDTR, double precision, dimension( ldb, * )B, integerLDB, double precisionSCALE, double precision, dimension( ldx, * )X, integerLDX, double precisionXNORM, integerINFO)

DLASY2 solves the Sylvester matrix equation where the matrices are of order 1 or 2.

Purpose:

 DLASY2 solves for the N1 by N2 matrix X, 1 <= N1,N2 <= 2, in

 op(TL)*X + ISGN*X*op(TR) = SCALE*B,

 where TL is N1 by N1, TR is N2 by N2, B is N1 by N2, and ISGN = 1 or

 -1. op(T) = T or T**T, where T**T denotes the transpose of T.

 

Parameters:

LTRANL

 LTRANL is LOGICAL

 On entry, LTRANL specifies the op(TL):

 = .FALSE., op(TL) = TL,

 = .TRUE., op(TL) = TL**T.

LTRANR

 LTRANR is LOGICAL

 On entry, LTRANR specifies the op(TR):

 = .FALSE., op(TR) = TR,

 = .TRUE., op(TR) = TR**T.

ISGN

 ISGN is INTEGER

 On entry, ISGN specifies the sign of the equation

 as described before. ISGN may only be 1 or -1.

N1

 N1 is INTEGER

 On entry, N1 specifies the order of matrix TL.

 N1 may only be 0, 1 or 2.

N2

 N2 is INTEGER

 On entry, N2 specifies the order of matrix TR.

 N2 may only be 0, 1 or 2.

TL

 TL is DOUBLE PRECISION array, dimension (LDTL,2)

 On entry, TL contains an N1 by N1 matrix.

LDTL

 LDTL is INTEGER

 The leading dimension of the matrix TL. LDTL >= max(1,N1).

TR

 TR is DOUBLE PRECISION array, dimension (LDTR,2)

 On entry, TR contains an N2 by N2 matrix.

LDTR

 LDTR is INTEGER

 The leading dimension of the matrix TR. LDTR >= max(1,N2).

B

 B is DOUBLE PRECISION array, dimension (LDB,2)

 On entry, the N1 by N2 matrix B contains the right-hand

 side of the equation.

LDB

 LDB is INTEGER

 The leading dimension of the matrix B. LDB >= max(1,N1).

SCALE

 SCALE is DOUBLE PRECISION

 On exit, SCALE contains the scale factor. SCALE is chosen

 less than or equal to 1 to prevent the solution overflowing.

X

 X is DOUBLE PRECISION array, dimension (LDX,2)

 On exit, X contains the N1 by N2 solution.

LDX

 LDX is INTEGER

 The leading dimension of the matrix X. LDX >= max(1,N1).

XNORM

 XNORM is DOUBLE PRECISION

 On exit, XNORM is the infinity-norm of the solution.

INFO

 INFO is INTEGER

 On exit, INFO is set to

 0: successful exit.

 1: TL and TR have too close eigenvalues, so TL or

 TR is perturbed to get a nonsingular equation.

 NOTE: In the interests of speed, this routine does not

 check the inputs for errors.

 

Author:

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Date:

September 2012

Definition at line 174 of file dlasy2.f.

Author

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