LAPACK 3.11.0
LAPACK: Linear Algebra PACKage
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◆ ssyl01()

subroutine ssyl01 ( real  thresh,
integer, dimension( 3 )  nfail,
real, dimension( 2 )  rmax,
integer, dimension( 2 )  ninfo,
integer  knt 
)

SSYL01

Purpose:
 SSYL01 tests STRSYL and STRSYL3, routines for solving the Sylvester matrix
 equation

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

 A and B are assumed to be in Schur canonical form, op() represents an
 optional transpose, and ISGN can be -1 or +1.  Scale is an output
 less than or equal to 1, chosen to avoid overflow in X.

 The test code verifies that the following residual does not exceed
 the provided threshold:

    norm(op(A)*X + ISGN*X*op(B) - scale*C) /
        (EPS*max(norm(A),norm(B))*norm(X))

 This routine complements SGET35 by testing with larger,
 random matrices, of which some require rescaling of X to avoid overflow.
Parameters
[in]THRESH
          THRESH is REAL
          A test will count as "failed" if the residual, computed as
          described above, exceeds THRESH.
[out]NFAIL
          NFAIL is INTEGER array, dimension (3)
          NFAIL(1) = No. of times residual STRSYL exceeds threshold THRESH
          NFAIL(2) = No. of times residual STRSYL3 exceeds threshold THRESH
          NFAIL(3) = No. of times STRSYL3 and STRSYL deviate
[out]RMAX
          RMAX is REAL, dimension (2)
          RMAX(1) = Value of the largest test ratio of STRSYL
          RMAX(2) = Value of the largest test ratio of STRSYL3
[out]NINFO
          NINFO is INTEGER array, dimension (2)
          NINFO(1) = No. of times STRSYL returns an expected INFO
          NINFO(2) = No. of times STRSYL3 returns an expected INFO
[out]KNT
          KNT is INTEGER
          Total number of examples tested.