1SLAZQ3(1)           LAPACK auxiliary routine (version 3.1)           SLAZQ3(1)
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NAME

6       SLAZQ3 - for deflation, computes a shift (TAU) and calls dqds
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SYNOPSIS

9       SUBROUTINE SLAZQ3( I0,  N0,  Z,  PP,  DMIN,  SIGMA, DESIG, QMAX, NFAIL,
10                          ITER, NDIV, IEEE, TTYPE, DMIN1, DMIN2, DN, DN1, DN2,
11                          TAU )
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13           LOGICAL        IEEE
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15           INTEGER        I0, ITER, N0, NDIV, NFAIL, PP, TTYPE
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17           REAL           DESIG,  DMIN,  DMIN1,  DMIN2,  DN,  DN1,  DN2, QMAX,
18                          SIGMA, TAU
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20           REAL           Z( * )
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PURPOSE

23       SLAZQ3 checks for deflation, computes a shift (TAU) and calls dqds.  In
24       case of failure it changes shifts, and tries again until output is pos‐
25       itive.
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ARGUMENTS

29       I0     (input) INTEGER
30              First index.
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32       N0     (input) INTEGER
33              Last index.
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35       Z      (input) REAL array, dimension ( 4*N )
36              Z holds the qd array.
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38       PP     (input) INTEGER
39              PP=0 for ping, PP=1 for pong.
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41       DMIN   (output) REAL
42              Minimum value of d.
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44       SIGMA  (output) REAL
45              Sum of shifts used in current segment.
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47       DESIG  (input/output) REAL
48              Lower order part of SIGMA
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50       QMAX   (input) REAL
51              Maximum value of q.
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53       NFAIL  (output) INTEGER
54              Number of times shift was too big.
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56       ITER   (output) INTEGER
57              Number of iterations.
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59       NDIV   (output) INTEGER
60              Number of divisions.
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62       IEEE   (input) LOGICAL
63              Flag for IEEE or non IEEE arithmetic (passed to SLASQ5).
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65       TTYPE  (input/output) INTEGER
66              Shift type.  TTYPE is passed as an argument in order to save its
67              value between calls to SLAZQ3
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69       DMIN1  (input/output) REAL
70              DMIN2    (input/output)  REAL  DN      (input/output)  REAL  DN1
71              (input/output)   REAL    DN2       (input/output)    REAL    TAU
72              (input/output)  REAL  These  are passed as arguments in order to
73              save their values between calls to SLAZQ3
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75              This is a thread safe version of  SLASQ3,  which  passes  TTYPE,
76              DMIN1,  DMIN2, DN, DN1. DN2 and TAU through the argument list in
77              place of declaring them in a SAVE statment.
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81 LAPACK auxiliary routine (versionOc3t.o1b)er 2006                        SLAZQ3(1)