NAME

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

SYNOPSIS

SUBROUTINE ZLAPLL( N, X, INCX, Y, INCY, SSMIN )

INTEGER INCX, INCY, N

DOUBLE PRECISION SSMIN

COMPLEX∗16 X( ∗ ), Y( ∗ )

#include <sunperf.h>

void zlapll(int n, doublecomplex ∗zx, int incx, doublecomplex ∗zy, int incy, double ∗ssmin) ;

PURPOSE

Given two column vectors X and Y, let
 
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) COMPLEX∗16 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) COMPLEX∗16 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 ).

SunOS 5.0  —  Last change: 10 Dec 1998