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.

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).

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

December 2016