dlapll(3S)

NAME
     DLAPLL - two column vectors X and Y, let  A = ( X Y )

SYNOPSIS
     SUBROUTINE DLAPLL( N, X, INCX, Y, INCY, SSMIN )

         INTEGER        INCX, INCY, N

         DOUBLE         PRECISION SSMIN

         DOUBLE         PRECISION X( * ), Y( * )

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
     Given two column vectors X and Y, let A = ( X Y ). The subroutine first
     computes the QR factorization of A = Q*R, and then computes the SVD of
     the 2-by-2 upper triangular matrix R.  The smaller singular value of R is
     returned in SSMIN, which is used as the measurement of the linear
     dependency of the vectors X and Y.


ARGUMENTS
     N       (input) INTEGER
             The length of the vectors X and Y.

     X       (input/output) DOUBLE PRECISION array,
             dimension (1+(N-1)*INCX) On entry, X contains the N-vector X.  On
             exit, X is overwritten.

     INCX    (input) INTEGER
             The increment between successive elements of X. INCX > 0.

     Y       (input/output) DOUBLE PRECISION array,
             dimension (1+(N-1)*INCY) On entry, Y contains the N-vector Y.  On
             exit, Y is overwritten.

     INCY    (input) INTEGER
             The increment between successive elements of Y. INCY > 0.
     SSMIN   (output) DOUBLE PRECISION
             The smallest singular value of the N-by-2 matrix A = ( X Y ).

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

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