slasq4(3S)

NAME
     SLASQ4 - compute an approximation TAU to the smallest eigenvalue using
     values of d from the previous transform

SYNOPSIS
     SUBROUTINE SLASQ4( I0, N0, Z, PP, N0IN, DMIN, DMIN1, DMIN2, DN, DN1, DN2,
                        TAU, TTYPE )

         INTEGER        I0, N0, N0IN, PP, TTYPE

         REAL           DMIN, DMIN1, DMIN2, DN, DN1, DN2, TAU

         REAL           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
     SLASQ4 computes an approximation TAU to the smallest eigenvalue using
     values of d from the previous transform.

ARGUMENTS
     I0    (input) INTEGER
           First index.

     N0    (input) INTEGER
           Last index.

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

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

     N0IN  (input) INTEGER
           The value of N0 at start of EIGTEST.

     DMIN  (input) REAL
           Minimum value of d.

     DMIN1 (input) REAL
           Minimum value of d, excluding D( N0 ).
     DMIN2 (input) REAL
           Minimum value of d, excluding D( N0 ) and D( N0-1 ).

     DN    (input) REAL
           d(N)

     DN1   (input) REAL
           d(N-1)

     DN2   (input) REAL
           d(N-2)

     TAU   (output) REAL
           This is the shift.

     TTYPE (output) INTEGER
           Shift type.


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

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