STRSYL (3) Linux Manual Page

strsyl.f –

Synopsis

Functions/Subroutines

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

Function/Subroutine Documentation

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.

Author

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