iparmq.f.html

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</span><span class="comment">*</span><span class="comment">                        by <a name="IPARMQ.122"></a><a href="iparmq.f.html#IPARMQ.1">IPARMQ</a>(ISPEC=15).  The default for
</span><span class="comment">*</span><span class="comment">                        (IHI-ILO+1).LE.500 is NS.  The default
</span><span class="comment">*</span><span class="comment">                        for (IHI-ILO+1).GT.500 is 3*NS/2.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">       <a name="IPARMQ.126"></a><a href="iparmq.f.html#IPARMQ.1">IPARMQ</a>(ISPEC=14) Nibble crossover point.  Default: 14.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">       <a name="IPARMQ.128"></a><a href="iparmq.f.html#IPARMQ.1">IPARMQ</a>(ISPEC=15) Number of simultaneous shifts, NS.
</span><span class="comment">*</span><span class="comment">                        a multi-shift QR iteration.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">                        If IHI-ILO+1 is ...
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">                        greater than      ...but less    ... the
</span><span class="comment">*</span><span class="comment">                        or equal to ...      than        default is
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">                                0               30       NS =   2+
</span><span class="comment">*</span><span class="comment">                               30               60       NS =   4+
</span><span class="comment">*</span><span class="comment">                               60              150       NS =  10
</span><span class="comment">*</span><span class="comment">                              150              590       NS =  **
</span><span class="comment">*</span><span class="comment">                              590             3000       NS =  64
</span><span class="comment">*</span><span class="comment">                             3000             6000       NS = 128
</span><span class="comment">*</span><span class="comment">                             6000             infinity   NS = 256
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">                    (+)  By default matrices of this order are
</span><span class="comment">*</span><span class="comment">                         passed to the implicit double shift routine
</span><span class="comment">*</span><span class="comment">                         xLAHQR.  See <a name="IPARMQ.146"></a><a href="iparmq.f.html#IPARMQ.1">IPARMQ</a>(ISPEC=12) above.   These
</span><span class="comment">*</span><span class="comment">                         values of NS are used only in case of a rare
</span><span class="comment">*</span><span class="comment">                         xLAHQR failure.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">                    (**) The asterisks (**) indicate an ad-hoc
</span><span class="comment">*</span><span class="comment">                         function increasing from 10 to 64.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">       <a name="IPARMQ.153"></a><a href="iparmq.f.html#IPARMQ.1">IPARMQ</a>(ISPEC=16) Select structured matrix multiply.
</span><span class="comment">*</span><span class="comment">                        (See ISPEC=16 above for details.)
</span><span class="comment">*</span><span class="comment">                        Default: 3.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     ================================================================
</span><span class="comment">*</span><span class="comment">     .. Parameters ..
</span>      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 )
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Local Scalars ..
</span>      INTEGER            NH, NS
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Intrinsic Functions ..
</span>      INTRINSIC          LOG, MAX, MOD, NINT, REAL
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Executable Statements ..
</span>      IF( ( ISPEC.EQ.ISHFTS ) .OR. ( ISPEC.EQ.INWIN ) .OR.
     $    ( ISPEC.EQ.IACC22 ) ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        ==== Set the number simultaneous shifts ====
</span><span class="comment">*</span><span class="comment">
</span>         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
<span class="comment">*</span><span class="comment">
</span>      IF( ISPEC.EQ.INMIN ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        ===== Matrices of order smaller than NMIN get sent
</span><span class="comment">*</span><span class="comment">        .     to xLAHQR, the classic double shift algorithm.
</span><span class="comment">*</span><span class="comment">        .     This must be at least 11. ====
</span><span class="comment">*</span><span class="comment">
</span>         <a name="IPARMQ.204"></a><a href="iparmq.f.html#IPARMQ.1">IPARMQ</a> = NMIN
<span class="comment">*</span><span class="comment">
</span>      ELSE IF( ISPEC.EQ.INIBL ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        ==== INIBL: skip a multi-shift qr iteration and
</span><span class="comment">*</span><span class="comment">        .    whenever aggressive early deflation finds
</span><span class="comment">*</span><span class="comment">        .    at least (NIBBLE*(window size)/100) deflations. ====
</span><span class="comment">*</span><span class="comment">
</span>         <a name="IPARMQ.212"></a><a href="iparmq.f.html#IPARMQ.1">IPARMQ</a> = NIBBLE
<span class="comment">*</span><span class="comment">
</span>      ELSE IF( ISPEC.EQ.ISHFTS ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        ==== NSHFTS: The number of simultaneous shifts =====
</span><span class="comment">*</span><span class="comment">
</span>         <a name="IPARMQ.218"></a><a href="iparmq.f.html#IPARMQ.1">IPARMQ</a> = NS
<span class="comment">*</span><span class="comment">
</span>      ELSE IF( ISPEC.EQ.INWIN ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        ==== NW: deflation window size.  ====
</span><span class="comment">*</span><span class="comment">
</span>         IF( NH.LE.KNWSWP ) THEN
            <a name="IPARMQ.225"></a><a href="iparmq.f.html#IPARMQ.1">IPARMQ</a> = NS
         ELSE
            <a name="IPARMQ.227"></a><a href="iparmq.f.html#IPARMQ.1">IPARMQ</a> = 3*NS / 2
         END IF
<span class="comment">*</span><span class="comment">
</span>      ELSE IF( ISPEC.EQ.IACC22 ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        ==== IACC22: Whether to accumulate reflections
</span><span class="comment">*</span><span class="comment">        .     before updating the far-from-diagonal elements
</span><span class="comment">*</span><span class="comment">        .     and whether to use 2-by-2 block structure while
</span><span class="comment">*</span><span class="comment">        .     doing it.  A small amount of work could be saved
</span><span class="comment">*</span><span class="comment">        .     by making this choice dependent also upon the
</span><span class="comment">*</span><span class="comment">        .     NH=IHI-ILO+1.
</span><span class="comment">*</span><span class="comment">
</span>         <a name="IPARMQ.239"></a><a href="iparmq.f.html#IPARMQ.1">IPARMQ</a> = 0
         IF( NS.GE.KACMIN )
     $      <a name="IPARMQ.241"></a><a href="iparmq.f.html#IPARMQ.1">IPARMQ</a> = 1
         IF( NS.GE.K22MIN )
     $      <a name="IPARMQ.243"></a><a href="iparmq.f.html#IPARMQ.1">IPARMQ</a> = 2
<span class="comment">*</span><span class="comment">
</span>      ELSE
<span class="comment">*</span><span class="comment">        ===== invalid value of ispec =====
</span>         <a name="IPARMQ.247"></a><a href="iparmq.f.html#IPARMQ.1">IPARMQ</a> = -1
<span class="comment">*</span><span class="comment">
</span>      END IF
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     ==== End of <a name="IPARMQ.251"></a><a href="iparmq.f.html#IPARMQ.1">IPARMQ</a> ====
</span><span class="comment">*</span><span class="comment">
</span>      END

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