iparmq()

integer function iparmq	(	integer	ISPEC,
		character, dimension( * )	NAME,
		character, dimension( * )	OPTS,
		integer	N,
		integer	ILO,
		integer	IHI,
		integer	LWORK
	)

Definition at line 301 of file ilaenv.f.

*
      INTEGER            INMIN, INWIN, INIBL, ISHFTS, IACC22
      parameter( inmin = 12, inwin = 13, inibl = 14,
     $                   ishfts = 15, iacc22 = 16 )
      INTEGER            NMIN, K22MIN, KACMIN, NIBBLE, KNWSWP
      parameter( nmin = 11, k22min = 14, kacmin = 14,
     $                   nibble = 14, knwswp = 500 )
      REAL               TWO
      parameter( two = 2.0 )
*     ..
*     .. Scalar Arguments ..
      INTEGER            IHI, ILO, ISPEC, LWORK, N
      CHARACTER          NAME*( * ), OPTS*( * )
*     ..
*     .. Local Scalars ..
      INTEGER            NH, NS
*     ..
*     .. Intrinsic Functions ..
      INTRINSIC          log, max, mod, nint, real
*     ..
*     .. Executable Statements ..
      IF( ( ispec.EQ.ishfts ) .OR. ( ispec.EQ.inwin ) .OR.
     $    ( ispec.EQ.iacc22 ) ) THEN
*
*        ==== Set the number simultaneous shifts ====
*
         nh = ihi - ilo + 1
         ns = 2
         IF( nh.GE.30 )
     $      ns = 4
         IF( nh.GE.60 )
     $      ns = 10
         IF( nh.GE.150 )
     $      ns = max( 10, nh / nint( log( real( nh ) ) / log( two ) ) )
         IF( nh.GE.590 )
     $      ns = 64
         IF( nh.GE.3000 )
     $      ns = 128
         IF( nh.GE.6000 )
     $      ns = 256
         ns = max( 2, ns-mod( ns, 2 ) )
      END IF
*
      IF( ispec.EQ.inmin ) THEN
*
*
*        ===== Matrices of order smaller than NMIN get sent
*        .     to LAHQR, the classic double shift algorithm.
*        .     This must be at least 11. ====
*
         iparmq = nmin
*
      ELSE IF( ispec.EQ.inibl ) THEN
*
*        ==== INIBL: skip a multi-shift qr iteration and
*        .    whenever aggressive early deflation finds
*        .    at least (NIBBLE*(window size)/100) deflations. ====
*
         iparmq = nibble
*
      ELSE IF( ispec.EQ.ishfts ) THEN
*
*        ==== NSHFTS: The number of simultaneous shifts =====
*
         iparmq = ns
*
      ELSE IF( ispec.EQ.inwin ) THEN
*
*        ==== NW: deflation window size.  ====
*
         IF( nh.LE.knwswp ) THEN
            iparmq = ns
         ELSE
            iparmq = 3*ns / 2
         END IF
*
      ELSE IF( ispec.EQ.iacc22 ) THEN
*
*        ==== IACC22: Whether to accumulate reflections
*        .     before updating the far-from-diagonal elements
*        .     and whether to use 2-by-2 block structure while
*        .     doing it.  A small amount of work could be saved
*        .     by making this choice dependent also upon the
*        .     NH=IHI-ILO+1.
*
         iparmq = 0
         IF( ns.GE.kacmin )
     $      iparmq = 1
         IF( ns.GE.k22min )
     $      iparmq = 2
*
      ELSE
*        ===== invalid value of ispec =====
         iparmq = -1
*
      END IF
*
*     ==== End of IPARMQ ====
*

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