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+      SUBROUTINE ZLARTG( F, G, CS, SN, R )
+*
+*  -- LAPACK auxiliary routine (version 3.1) --
+*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
+*     November 2006
+*
+*     .. Scalar Arguments ..
+      DOUBLE PRECISION   CS
+      COMPLEX*16         F, G, R, SN
+*     ..
+*
+*  Purpose
+*  =======
+*
+*  ZLARTG generates a plane rotation so that
+*
+*     [  CS  SN  ]     [ F ]     [ R ]
+*     [  __      ]  .  [   ]  =  [   ]   where CS**2 + |SN|**2 = 1.
+*     [ -SN  CS  ]     [ G ]     [ 0 ]
+*
+*  This is a faster version of the BLAS1 routine ZROTG, except for
+*  the following differences:
+*     F and G are unchanged on return.
+*     If G=0, then CS=1 and SN=0.
+*     If F=0, then CS=0 and SN is chosen so that R is real.
+*
+*  Arguments
+*  =========
+*
+*  F       (input) COMPLEX*16
+*          The first component of vector to be rotated.
+*
+*  G       (input) COMPLEX*16
+*          The second component of vector to be rotated.
+*
+*  CS      (output) DOUBLE PRECISION
+*          The cosine of the rotation.
+*
+*  SN      (output) COMPLEX*16
+*          The sine of the rotation.
+*
+*  R       (output) COMPLEX*16
+*          The nonzero component of the rotated vector.
+*
+*  Further Details
+*  ======= =======
+*
+*  3-5-96 - Modified with a new algorithm by W. Kahan and J. Demmel
+*
+*  This version has a few statements commented out for thread safety
+*  (machine parameters are computed on each entry). 10 feb 03, SJH.
+*
+*  =====================================================================
+*
+*     .. Parameters ..
+      DOUBLE PRECISION   TWO, ONE, ZERO
+      PARAMETER          ( TWO = 2.0D+0, ONE = 1.0D+0, ZERO = 0.0D+0 )
+      COMPLEX*16         CZERO
+      PARAMETER          ( CZERO = ( 0.0D+0, 0.0D+0 ) )
+*     ..
+*     .. Local Scalars ..
+*     LOGICAL            FIRST
+      INTEGER            COUNT, I
+      DOUBLE PRECISION   D, DI, DR, EPS, F2, F2S, G2, G2S, SAFMIN,
+     $                   SAFMN2, SAFMX2, SCALE
+      COMPLEX*16         FF, FS, GS
+*     ..
+*     .. External Functions ..
+      DOUBLE PRECISION   DLAMCH, DLAPY2
+      EXTERNAL           DLAMCH, DLAPY2
+*     ..
+*     .. Intrinsic Functions ..
+      INTRINSIC          ABS, DBLE, DCMPLX, DCONJG, DIMAG, INT, LOG,
+     $                   MAX, SQRT
+*     ..
+*     .. Statement Functions ..
+      DOUBLE PRECISION   ABS1, ABSSQ
+*     ..
+*     .. Save statement ..
+*     SAVE               FIRST, SAFMX2, SAFMIN, SAFMN2
+*     ..
+*     .. Data statements ..
+*     DATA               FIRST / .TRUE. /
+*     ..
+*     .. Statement Function definitions ..
+      ABS1( FF ) = MAX( ABS( DBLE( FF ) ), ABS( DIMAG( FF ) ) )
+      ABSSQ( FF ) = DBLE( FF )**2 + DIMAG( FF )**2
+*     ..
+*     .. Executable Statements ..
+*
+*     IF( FIRST ) THEN
+         SAFMIN = DLAMCH( 'S' )
+         EPS = DLAMCH( 'E' )
+         SAFMN2 = DLAMCH( 'B' )**INT( LOG( SAFMIN / EPS ) /
+     $            LOG( DLAMCH( 'B' ) ) / TWO )
+         SAFMX2 = ONE / SAFMN2
+*        FIRST = .FALSE.
+*     END IF
+      SCALE = MAX( ABS1( F ), ABS1( G ) )
+      FS = F
+      GS = G
+      COUNT = 0
+      IF( SCALE.GE.SAFMX2 ) THEN
+   10    CONTINUE
+         COUNT = COUNT + 1
+         FS = FS*SAFMN2
+         GS = GS*SAFMN2
+         SCALE = SCALE*SAFMN2
+         IF( SCALE.GE.SAFMX2 )
+     $      GO TO 10
+      ELSE IF( SCALE.LE.SAFMN2 ) THEN
+         IF( G.EQ.CZERO ) THEN
+            CS = ONE
+            SN = CZERO
+            R = F
+            RETURN
+         END IF
+   20    CONTINUE
+         COUNT = COUNT - 1
+         FS = FS*SAFMX2
+         GS = GS*SAFMX2
+         SCALE = SCALE*SAFMX2
+         IF( SCALE.LE.SAFMN2 )
+     $      GO TO 20
+      END IF
+      F2 = ABSSQ( FS )
+      G2 = ABSSQ( GS )
+      IF( F2.LE.MAX( G2, ONE )*SAFMIN ) THEN
+*
+*        This is a rare case: F is very small.
+*
+         IF( F.EQ.CZERO ) THEN
+            CS = ZERO
+            R = DLAPY2( DBLE( G ), DIMAG( G ) )
+*           Do complex/real division explicitly with two real divisions
+            D = DLAPY2( DBLE( GS ), DIMAG( GS ) )
+            SN = DCMPLX( DBLE( GS ) / D, -DIMAG( GS ) / D )
+            RETURN
+         END IF
+         F2S = DLAPY2( DBLE( FS ), DIMAG( FS ) )
+*        G2 and G2S are accurate
+*        G2 is at least SAFMIN, and G2S is at least SAFMN2
+         G2S = SQRT( G2 )
+*        Error in CS from underflow in F2S is at most
+*        UNFL / SAFMN2 .lt. sqrt(UNFL*EPS) .lt. EPS
+*        If MAX(G2,ONE)=G2, then F2 .lt. G2*SAFMIN,
+*        and so CS .lt. sqrt(SAFMIN)
+*        If MAX(G2,ONE)=ONE, then F2 .lt. SAFMIN
+*        and so CS .lt. sqrt(SAFMIN)/SAFMN2 = sqrt(EPS)
+*        Therefore, CS = F2S/G2S / sqrt( 1 + (F2S/G2S)**2 ) = F2S/G2S
+         CS = F2S / G2S
+*        Make sure abs(FF) = 1
+*        Do complex/real division explicitly with 2 real divisions
+         IF( ABS1( F ).GT.ONE ) THEN
+            D = DLAPY2( DBLE( F ), DIMAG( F ) )
+            FF = DCMPLX( DBLE( F ) / D, DIMAG( F ) / D )
+         ELSE
+            DR = SAFMX2*DBLE( F )
+            DI = SAFMX2*DIMAG( F )
+            D = DLAPY2( DR, DI )
+            FF = DCMPLX( DR / D, DI / D )
+         END IF
+         SN = FF*DCMPLX( DBLE( GS ) / G2S, -DIMAG( GS ) / G2S )
+         R = CS*F + SN*G
+      ELSE
+*
+*        This is the most common case.
+*        Neither F2 nor F2/G2 are less than SAFMIN
+*        F2S cannot overflow, and it is accurate
+*
+         F2S = SQRT( ONE+G2 / F2 )
+*        Do the F2S(real)*FS(complex) multiply with two real multiplies
+         R = DCMPLX( F2S*DBLE( FS ), F2S*DIMAG( FS ) )
+         CS = ONE / F2S
+         D = F2 + G2
+*        Do complex/real division explicitly with two real divisions
+         SN = DCMPLX( DBLE( R ) / D, DIMAG( R ) / D )
+         SN = SN*DCONJG( GS )
+         IF( COUNT.NE.0 ) THEN
+            IF( COUNT.GT.0 ) THEN
+               DO 30 I = 1, COUNT
+                  R = R*SAFMX2
+   30          CONTINUE
+            ELSE
+               DO 40 I = 1, -COUNT
+                  R = R*SAFMN2
+   40          CONTINUE
+            END IF
+         END IF
+      END IF
+      RETURN
+*
+*     End of ZLARTG
+*
+      END