/*  -- translated by f2c (version 20100827).
   You must link the resulting object file with libf2c:
	on Microsoft Windows system, link with libf2c.lib;
	on Linux or Unix systems, link with .../path/to/libf2c.a -lm
	or, if you install libf2c.a in a standard place, with -lf2c -lm
	-- in that order, at the end of the command line, as in
		cc *.o -lf2c -lm
	Source for libf2c is in /netlib/f2c/libf2c.zip, e.g.,

		http://www.netlib.org/f2c/libf2c.zip
*/

#include "f2c.h"

integer igraphiparmq_(integer *ispec, char *name__, char *opts, integer *n, integer 
	*ilo, integer *ihi, integer *lwork)
{
    /* System generated locals */
    integer ret_val, i__1, i__2;
    real r__1;

    /* Builtin functions */
    double log(doublereal);
    integer i_nint(real *);

    /* Local variables */
    integer nh, ns;


/*  -- LAPACK auxiliary routine (version 3.2) --   
    -- LAPACK is a software package provided by Univ. of Tennessee,    --   
    -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--   
       November 2006   


    Purpose   
    =======   

         This program sets problem and machine dependent parameters   
         useful for xHSEQR and its subroutines. It is called whenever   
         ILAENV is called with 12 <= ISPEC <= 16   

    Arguments   
    =========   

         ISPEC  (input) integer scalar   
                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.GT.(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 sweep,   
                              xLAQR5 does not accumulate reflections and   
                              does not use matrix-matrix multiply to   
                              update the far-from-diagonal matrix   
                              entries.   
                          1:  During the multi-shift QR sweep,   
                              xLAQR5 and/or xLAQRaccumulates reflections and uses   
                              matrix-matrix multiply to update the   
                              far-from-diagonal matrix entries.   
                          2:  During the multi-shift QR sweep.   
                              xLAQR5 accumulates reflections and takes   
                              advantage of 2-by-2 block structure 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.)   

         NAME    (input) character string   
                 Name of the calling subroutine   

         OPTS    (input) character string   
                 This is a concatenation of the string arguments to   
                 TTQRE.   

         N       (input) integer scalar   
                 N is the order of the Hessenberg matrix H.   

         ILO     (input) INTEGER   
         IHI     (input) INTEGER   
                 It is assumed that H is already upper triangular   
                 in rows and columns 1:ILO-1 and IHI+1:N.   

         LWORK   (input) integer scalar   
                 The amount of workspace available.   

    Further Details   
    ===============   

         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).LE.500 is NS.  The default   
                          for (IHI-ILO+1).GT.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.   

       ================================================================ */
    if (*ispec == 15 || *ispec == 13 || *ispec == 16) {

/*        ==== Set the number simultaneous shifts ==== */

	nh = *ihi - *ilo + 1;
	ns = 2;
	if (nh >= 30) {
	    ns = 4;
	}
	if (nh >= 60) {
	    ns = 10;
	}
	if (nh >= 150) {
/* Computing MAX */
	    r__1 = log((real) nh) / log(2.f);
	    i__1 = 10, i__2 = nh / i_nint(&r__1);
	    ns = max(i__1,i__2);
	}
	if (nh >= 590) {
	    ns = 64;
	}
	if (nh >= 3000) {
	    ns = 128;
	}
	if (nh >= 6000) {
	    ns = 256;
	}
/* Computing MAX */
	i__1 = 2, i__2 = ns - ns % 2;
	ns = max(i__1,i__2);
    }

    if (*ispec == 12) {


/*        ===== Matrices of order smaller than NMIN get sent   
          .     to xLAHQR, the classic double shift algorithm.   
          .     This must be at least 11. ==== */

	ret_val = 75;

    } else if (*ispec == 14) {

/*        ==== INIBL: skip a multi-shift qr iteration and   
          .    whenever aggressive early deflation finds   
          .    at least (NIBBLE*(window size)/100) deflations. ==== */

	ret_val = 14;

    } else if (*ispec == 15) {

/*        ==== NSHFTS: The number of simultaneous shifts ===== */

	ret_val = ns;

    } else if (*ispec == 13) {

/*        ==== NW: deflation window size.  ==== */

	if (nh <= 500) {
	    ret_val = ns;
	} else {
	    ret_val = ns * 3 / 2;
	}

    } else if (*ispec == 16) {

/*        ==== 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. */

	ret_val = 0;
	if (ns >= 14) {
	    ret_val = 1;
	}
	if (ns >= 14) {
	    ret_val = 2;
	}

    } else {
/*        ===== invalid value of ispec ===== */
	ret_val = -1;

    }

/*     ==== End of IPARMQ ==== */

    return ret_val;
} /* igraphiparmq_ */

