CXML
        	    
LAPACK version 3.0
slasq2(3)

PURPOSE
  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

SYNTAX
  SUBROUTINE SLASQ2( N, Z, INFO )

      INTEGER	     INFO, N

      REAL	     Z( * )

DESCRIPTION
  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 (program 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).