*> \brief \b IPARMQ * * =========== DOCUMENTATION =========== * * Online html documentation available at * http://www.netlib.org/lapack/explore-html/ * *> \htmlonly *> Download IPARMQ + dependencies *> *> [TGZ] *> *> [ZIP] *> *> [TXT] *> \endhtmlonly * * Definition: * =========== * * INTEGER FUNCTION IPARMQ( ISPEC, NAME, OPTS, N, ILO, IHI, LWORK ) * * .. Scalar Arguments .. * INTEGER IHI, ILO, ISPEC, LWORK, N * CHARACTER NAME*( * ), OPTS*( * ) * * *> \par Purpose: * ============= *> *> \verbatim *> *> This program sets problem and machine dependent parameters *> useful for xHSEQR and related subroutines for eigenvalue *> problems. It is called whenever *> IPARMQ is called with 12 <= ISPEC <= 16 *> \endverbatim * * Arguments: * ========== * *> \param[in] ISPEC *> \verbatim *> ISPEC is INTEGER *> ISPEC specifies which tunable parameter IPARMQ should *> return. *> *> ISPEC=12: (INMIN) Matrices of order nmin or less *> are sent directly to xLAHQR, the implicit *> double shift QR algorithm. NMIN must be *> at least 11. *> *> ISPEC=13: (INWIN) Size of the deflation window. *> This is best set greater than or equal to *> the number of simultaneous shifts NS. *> Larger matrices benefit from larger deflation *> windows. *> *> ISPEC=14: (INIBL) Determines when to stop nibbling and *> invest in an (expensive) multi-shift QR sweep. *> If the aggressive early deflation subroutine *> finds LD converged eigenvalues from an order *> NW deflation window and LD > (NW*NIBBLE)/100, *> then the next QR sweep is skipped and early *> deflation is applied immediately to the *> remaining active diagonal block. Setting *> IPARMQ(ISPEC=14) = 0 causes TTQRE to skip a *> multi-shift QR sweep whenever early deflation *> finds a converged eigenvalue. Setting *> IPARMQ(ISPEC=14) greater than or equal to 100 *> prevents TTQRE from skipping a multi-shift *> QR sweep. *> *> ISPEC=15: (NSHFTS) The number of simultaneous shifts in *> a multi-shift QR iteration. *> *> ISPEC=16: (IACC22) IPARMQ is set to 0, 1 or 2 with the *> following meanings. *> 0: During the multi-shift QR/QZ sweep, *> blocked eigenvalue reordering, blocked *> Hessenberg-triangular reduction, *> reflections and/or rotations are not *> accumulated when updating the *> far-from-diagonal matrix entries. *> 1: During the multi-shift QR/QZ sweep, *> blocked eigenvalue reordering, blocked *> Hessenberg-triangular reduction, *> reflections and/or rotations are *> accumulated, and matrix-matrix *> multiplication is used to update the *> far-from-diagonal matrix entries. *> 2: During the multi-shift QR/QZ sweep, *> blocked eigenvalue reordering, blocked *> Hessenberg-triangular reduction, *> reflections and/or rotations are *> accumulated, and 2-by-2 block structure *> is exploited during matrix-matrix *> multiplies. *> (If xTRMM is slower than xGEMM, then *> IPARMQ(ISPEC=16)=1 may be more efficient than *> IPARMQ(ISPEC=16)=2 despite the greater level of *> arithmetic work implied by the latter choice.) *> \endverbatim *> *> \param[in] NAME *> \verbatim *> NAME is CHARACTER string *> Name of the calling subroutine *> \endverbatim *> *> \param[in] OPTS *> \verbatim *> OPTS is CHARACTER string *> This is a concatenation of the string arguments to *> TTQRE. *> \endverbatim *> *> \param[in] N *> \verbatim *> N is INTEGER *> N is the order of the Hessenberg matrix H. *> \endverbatim *> *> \param[in] ILO *> \verbatim *> ILO is INTEGER *> \endverbatim *> *> \param[in] IHI *> \verbatim *> IHI is INTEGER *> It is assumed that H is already upper triangular *> in rows and columns 1:ILO-1 and IHI+1:N. *> \endverbatim *> *> \param[in] LWORK *> \verbatim *> LWORK is INTEGER *> The amount of workspace available. *> \endverbatim * * Authors: * ======== * *> \author Univ. of Tennessee *> \author Univ. of California Berkeley *> \author Univ. of Colorado Denver *> \author NAG Ltd. * *> \date June 2017 * *> \ingroup OTHERauxiliary * *> \par Further Details: * ===================== *> *> \verbatim *> *> Little is known about how best to choose these parameters. *> It is possible to use different values of the parameters *> for each of CHSEQR, DHSEQR, SHSEQR and ZHSEQR. *> *> It is probably best to choose different parameters for *> different matrices and different parameters at different *> times during the iteration, but this has not been *> implemented --- yet. *> *> *> The best choices of most of the parameters depend *> in an ill-understood way on the relative execution *> rate of xLAQR3 and xLAQR5 and on the nature of each *> particular eigenvalue problem. Experiment may be the *> only practical way to determine which choices are most *> effective. *> *> Following is a list of default values supplied by IPARMQ. *> These defaults may be adjusted in order to attain better *> performance in any particular computational environment. *> *> IPARMQ(ISPEC=12) The xLAHQR vs xLAQR0 crossover point. *> Default: 75. (Must be at least 11.) *> *> IPARMQ(ISPEC=13) Recommended deflation window size. *> This depends on ILO, IHI and NS, the *> number of simultaneous shifts returned *> by IPARMQ(ISPEC=15). The default for *> (IHI-ILO+1) <= 500 is NS. The default *> for (IHI-ILO+1) > 500 is 3*NS/2. *> *> IPARMQ(ISPEC=14) Nibble crossover point. Default: 14. *> *> IPARMQ(ISPEC=15) Number of simultaneous shifts, NS. *> a multi-shift QR iteration. *> *> If IHI-ILO+1 is ... *> *> greater than ...but less ... the *> or equal to ... than default is *> *> 0 30 NS = 2+ *> 30 60 NS = 4+ *> 60 150 NS = 10 *> 150 590 NS = ** *> 590 3000 NS = 64 *> 3000 6000 NS = 128 *> 6000 infinity NS = 256 *> *> (+) By default matrices of this order are *> passed to the implicit double shift routine *> xLAHQR. See IPARMQ(ISPEC=12) above. These *> values of NS are used only in case of a rare *> xLAHQR failure. *> *> (**) The asterisks (**) indicate an ad-hoc *> function increasing from 10 to 64. *> *> IPARMQ(ISPEC=16) Select structured matrix multiply. *> (See ISPEC=16 above for details.) *> Default: 3. *> \endverbatim *> * ===================================================================== INTEGER FUNCTION IPARMQ( ISPEC, NAME, OPTS, N, ILO, IHI, LWORK ) * * -- LAPACK auxiliary routine (version 3.7.1) -- * -- LAPACK is a software package provided by Univ. of Tennessee, -- * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- * June 2017 * * .. Scalar Arguments .. INTEGER IHI, ILO, ISPEC, LWORK, N CHARACTER NAME*( * ), OPTS*( * ) * * ================================================================ * .. Parameters .. 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 = 75, K22MIN = 14, KACMIN = 14, $ NIBBLE = 14, KNWSWP = 500 ) REAL TWO PARAMETER ( TWO = 2.0 ) * .. * .. Local Scalars .. INTEGER NH, NS INTEGER I, IC, IZ CHARACTER SUBNAM*6 * .. * .. 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 xLAHQR, 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. * * * Convert NAME to upper case if the first character is lower case. * IPARMQ = 0 SUBNAM = NAME IC = ICHAR( SUBNAM( 1: 1 ) ) IZ = ICHAR( 'Z' ) IF( IZ.EQ.90 .OR. IZ.EQ.122 ) THEN * * ASCII character set * IF( IC.GE.97 .AND. IC.LE.122 ) THEN SUBNAM( 1: 1 ) = CHAR( IC-32 ) DO I = 2, 6 IC = ICHAR( SUBNAM( I: I ) ) IF( IC.GE.97 .AND. IC.LE.122 ) $ SUBNAM( I: I ) = CHAR( IC-32 ) END DO END IF * ELSE IF( IZ.EQ.233 .OR. IZ.EQ.169 ) THEN * * EBCDIC character set * IF( ( IC.GE.129 .AND. IC.LE.137 ) .OR. $ ( IC.GE.145 .AND. IC.LE.153 ) .OR. $ ( IC.GE.162 .AND. IC.LE.169 ) ) THEN SUBNAM( 1: 1 ) = CHAR( IC+64 ) DO I = 2, 6 IC = ICHAR( SUBNAM( I: I ) ) IF( ( IC.GE.129 .AND. IC.LE.137 ) .OR. $ ( IC.GE.145 .AND. IC.LE.153 ) .OR. $ ( IC.GE.162 .AND. IC.LE.169 ) )SUBNAM( I: $ I ) = CHAR( IC+64 ) END DO END IF * ELSE IF( IZ.EQ.218 .OR. IZ.EQ.250 ) THEN * * Prime machines: ASCII+128 * IF( IC.GE.225 .AND. IC.LE.250 ) THEN SUBNAM( 1: 1 ) = CHAR( IC-32 ) DO I = 2, 6 IC = ICHAR( SUBNAM( I: I ) ) IF( IC.GE.225 .AND. IC.LE.250 ) $ SUBNAM( I: I ) = CHAR( IC-32 ) END DO END IF END IF * IF( SUBNAM( 2:6 ).EQ.'GGHRD' .OR. $ SUBNAM( 2:6 ).EQ.'GGHD3' ) THEN IPARMQ = 1 IF( NH.GE.K22MIN ) $ IPARMQ = 2 ELSE IF ( SUBNAM( 4:6 ).EQ.'EXC' ) THEN IF( NH.GE.KACMIN ) $ IPARMQ = 1 IF( NH.GE.K22MIN ) $ IPARMQ = 2 ELSE IF ( SUBNAM( 2:6 ).EQ.'HSEQR' .OR. $ SUBNAM( 2:5 ).EQ.'LAQR' ) THEN IF( NS.GE.KACMIN ) $ IPARMQ = 1 IF( NS.GE.K22MIN ) $ IPARMQ = 2 END IF * ELSE * ===== invalid value of ispec ===== IPARMQ = -1 * END IF * * ==== End of IPARMQ ==== * END