redhat man page for slasq2

SLASQ2(l)								 )								 SLASQ2(l)

NAME
       SLASQ2  - compute all the eigenvalues of the symmetric positive definite tridiagonal matrix associated with the qd array Z to high relative
       accuracy are computed to high relative accuracy, in the absence of denormalization, underflow and overflow

SYNOPSIS
       SUBROUTINE SLASQ2( N, Z, INFO )

	   INTEGER	  INFO, N

	   REAL 	  Z( * )

PURPOSE
       SLASQ2 computes all the eigenvalues of the symmetric positive definite tridiagonal matrix associated with the qd array Z to  high  relative
       accuracy  are  computed	to high relative accuracy, in the absence of denormalization, underflow and overflow.  To see the relation of Z to
       the tridiagonal matrix, let L be a unit lower bidiagonal matrix with subdiagonals Z(2,4,6,,..) and let U be an upper bidiagonal matrix with
       1's above and diagonal Z(1,3,5,,..). The tridiagonal is L*U or, if you prefer, the symmetric tridiagonal to which it is similar.

       Note  :	SLASQ2 defines a logical variable, IEEE, which is true on machines which follow ieee-754 floating-point standard in their handling
       of infinities and NaNs, and false otherwise. This variable is passed to SLASQ3.

ARGUMENTS
       N     (input) INTEGER
	     The number of rows and columns in the matrix. N >= 0.

       Z     (workspace) REAL array, dimension ( 4*N )
	     On entry Z holds the qd array. On exit, entries 1 to N hold the eigenvalues in decreasing order, Z( 2*N+1 ) holds the trace,  and	Z(
	     2*N+2  )  holds the sum of the eigenvalues. If N > 2, then Z( 2*N+3 ) holds the iteration count, Z( 2*N+4 ) holds NDIVS/NIN^2, and Z(
	     2*N+5 ) holds the percentage of shifts that failed.

       INFO  (output) INTEGER
	     = 0: successful exit
	     < 0: if the i-th argument is a scalar and had an illegal value, then INFO = -i, if the i-th argument is an array and the j-entry  had
	     an  illegal  value,  then	INFO  = -(i*100+j) > 0: the algorithm failed = 1, a split was marked by a positive value in E = 2, current
	     block of Z not diagonalized after 30*N iterations (in inner while loop) = 3, termination criterion of outer while loop not met  (pro-
	     gram created more than N unreduced blocks)

FURTHER DETAILS
       The shifts are accumulated in SIGMA. Iteration count is in ITER.  Ping-pong is controlled by PP (alternates between 0 and 1).

LAPACK version 3.0						   15 June 2000 							 SLASQ2(l)