slasy2.f - Man Page

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.

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

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

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 REAL 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 REAL 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 REAL 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 REAL
          On exit, SCALE contains the scale factor. SCALE is chosen
          less than or equal to 1 to prevent the solution overflowing.

X

          X is REAL 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 REAL
          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.

Definition at line 172 of file slasy2.f.