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slasy2.f File Reference

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Functions/Subroutines

subroutine slasy2 (LTRANL, LTRANR, ISGN, N1, N2, TL, LDTL, TR, LDTR, B, LDB, SCALE, X, LDX, XNORM, INFO)
 SLASY2 solves the Sylvester matrix equation where the matrices are of order 1 or 2. More...
 

Function/Subroutine Documentation

subroutine slasy2 ( logical  LTRANL,
logical  LTRANR,
integer  ISGN,
integer  N1,
integer  N2,
real, dimension( ldtl, * )  TL,
integer  LDTL,
real, dimension( ldtr, * )  TR,
integer  LDTR,
real, dimension( ldb, * )  B,
integer  LDB,
real  SCALE,
real, dimension( ldx, * )  X,
integer  LDX,
real  XNORM,
integer  INFO 
)

SLASY2 solves the Sylvester matrix equation where the matrices are of order 1 or 2.

Download SLASY2 + dependencies [TGZ] [ZIP] [TXT]

Purpose:
 SLASY2 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
[in]LTRANL
          LTRANL is LOGICAL
          On entry, LTRANL specifies the op(TL):
             = .FALSE., op(TL) = TL,
             = .TRUE., op(TL) = TL**T.
[in]LTRANR
          LTRANR is LOGICAL
          On entry, LTRANR specifies the op(TR):
            = .FALSE., op(TR) = TR,
            = .TRUE., op(TR) = TR**T.
[in]ISGN
          ISGN is INTEGER
          On entry, ISGN specifies the sign of the equation
          as described before. ISGN may only be 1 or -1.
[in]N1
          N1 is INTEGER
          On entry, N1 specifies the order of matrix TL.
          N1 may only be 0, 1 or 2.
[in]N2
          N2 is INTEGER
          On entry, N2 specifies the order of matrix TR.
          N2 may only be 0, 1 or 2.
[in]TL
          TL is REAL array, dimension (LDTL,2)
          On entry, TL contains an N1 by N1 matrix.
[in]LDTL
          LDTL is INTEGER
          The leading dimension of the matrix TL. LDTL >= max(1,N1).
[in]TR
          TR is REAL array, dimension (LDTR,2)
          On entry, TR contains an N2 by N2 matrix.
[in]LDTR
          LDTR is INTEGER
          The leading dimension of the matrix TR. LDTR >= max(1,N2).
[in]B
          B is REAL array, dimension (LDB,2)
          On entry, the N1 by N2 matrix B contains the right-hand
          side of the equation.
[in]LDB
          LDB is INTEGER
          The leading dimension of the matrix B. LDB >= max(1,N1).
[out]SCALE
          SCALE is REAL
          On exit, SCALE contains the scale factor. SCALE is chosen
          less than or equal to 1 to prevent the solution overflowing.
[out]X
          X is REAL array, dimension (LDX,2)
          On exit, X contains the N1 by N2 solution.
[in]LDX
          LDX is INTEGER
          The leading dimension of the matrix X. LDX >= max(1,N1).
[out]XNORM
          XNORM is REAL
          On exit, XNORM is the infinity-norm of the solution.
[out]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 slasy2.f.

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