dlasq3(3S)

NAME
     DLASQ3 - check for deflation, computes a shift (TAU) and calls dqds

SYNOPSIS
     SUBROUTINE DLASQ3( I0, N0, Z, PP, DMIN, SIGMA, DESIG, QMAX, NFAIL, ITER,
                        NDIV, IEEE )

         LOGICAL        IEEE

         INTEGER        I0, ITER, N0, NDIV, NFAIL, PP

         DOUBLE         PRECISION DESIG, DMIN, QMAX, SIGMA

         DOUBLE         PRECISION Z( * )

IMPLEMENTATION
     These routines are part of the SCSL Scientific Library and can be loaded
     using either the -lscs or the -lscs_mp option.  The -lscs_mp option
     directs the linker to use the multi-processor version of the library.

     When linking to SCSL with -lscs or -lscs_mp, the default integer size is
     4 bytes (32 bits). Another version of SCSL is available in which integers
     are 8 bytes (64 bits).  This version allows the user access to larger
     memory sizes and helps when porting legacy Cray codes.  It can be loaded
     by using the -lscs_i8 option or the -lscs_i8_mp option. A program may use
     only one of the two versions; 4-byte integer and 8-byte integer library
     calls cannot be mixed.

PURPOSE
     DLASQ3 checks for deflation, computes a shift (TAU) and calls dqds. In
     case of failure it changes shifts, and tries again until output is
     positive.


ARGUMENTS
     I0     (input) INTEGER
            First index.

     N0     (input) INTEGER
            Last index.

     Z      (input) DOUBLE PRECISION array, dimension ( 4*N )
            Z holds the qd array.

     PP     (input) INTEGER
            PP=0 for ping, PP=1 for pong.

     DMIN   (output) DOUBLE PRECISION
            Minimum value of d.
     SIGMA  (output) DOUBLE PRECISION
            Sum of shifts used in current segment.

     DESIG  (input/output) DOUBLE PRECISION
            Lower order part of SIGMA

     QMAX   (input) DOUBLE PRECISION
            Maximum value of q.

     NFAIL  (output) INTEGER
            Number of times shift was too big.

     ITER   (output) INTEGER
            Number of iterations.

     NDIV   (output) INTEGER
            Number of divisions.

     TTYPE  (output) INTEGER
            Shift type.

     IEEE   (input) LOGICAL
            Flag for IEEE or non IEEE arithmetic (passed to DLASQ5).

SEE ALSO
     INTRO_LAPACK(3S), INTRO_SCSL(3S)

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