strsyl (3)

Functions/Subroutines

subroutine strsyl (TRANA, TRANB, ISGN, M, N, A, LDA, B, LDB, C, LDC, SCALE, INFO)

STRSYL

subroutine strsyl (characterTRANA, characterTRANB, integerISGN, integerM, integerN, real, dimension( lda, * )A, integerLDA, real, dimension( ldb, * )B, integerLDB, real, dimension( ldc, * )C, integerLDC, realSCALE, integerINFO)

STRSYL

Purpose:

 STRSYL solves the real Sylvester matrix equation:

    op(A)*X + X*op(B) = scale*C or
    op(A)*X - X*op(B) = scale*C,

 where op(A) = A or A**T, and  A and B are both upper quasi-
 triangular. A is M-by-M and B is N-by-N; the right hand side C and
 the solution X are M-by-N; and scale is an output scale factor, set
 <= 1 to avoid overflow in X.

 A and B must be in Schur canonical form (as returned by SHSEQR), that
 is, block upper triangular with 1-by-1 and 2-by-2 diagonal blocks;
 each 2-by-2 diagonal block has its diagonal elements equal and its
 off-diagonal elements of opposite sign.

Parameters:

TRANA

          TRANA is CHARACTER*1
          Specifies the option op(A):
          = 'N': op(A) = A    (No transpose)
          = 'T': op(A) = A**T (Transpose)
          = 'C': op(A) = A**H (Conjugate transpose = Transpose)

TRANB

          TRANB is CHARACTER*1
          Specifies the option op(B):
          = 'N': op(B) = B    (No transpose)
          = 'T': op(B) = B**T (Transpose)
          = 'C': op(B) = B**H (Conjugate transpose = Transpose)

ISGN

          ISGN is INTEGER
          Specifies the sign in the equation:
          = +1: solve op(A)*X + X*op(B) = scale*C
          = -1: solve op(A)*X - X*op(B) = scale*C

M

          M is INTEGER
          The order of the matrix A, and the number of rows in the
          matrices X and C. M >= 0.

N

          N is INTEGER
          The order of the matrix B, and the number of columns in the
          matrices X and C. N >= 0.

A

          A is REAL array, dimension (LDA,M)
          The upper quasi-triangular matrix A, in Schur canonical form.

LDA

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

B

          B is REAL array, dimension (LDB,N)
          The upper quasi-triangular matrix B, in Schur canonical form.

LDB

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

C

          C is REAL array, dimension (LDC,N)
          On entry, the M-by-N right hand side matrix C.
          On exit, C is overwritten by the solution matrix X.

LDC

          LDC is INTEGER
          The leading dimension of the array C. LDC >= max(1,M)

SCALE

          SCALE is REAL
          The scale factor, scale, set <= 1 to avoid overflow in X.

INFO

          INFO is INTEGER
          = 0: successful exit
          < 0: if INFO = -i, the i-th argument had an illegal value
          = 1: A and B have common or very close eigenvalues; perturbed
               values were used to solve the equation (but the matrices
               A and B are unchanged).

Author:

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Date:

November 2011

Definition at line 164 of file strsyl.f.

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