Unix/Linux Go Back    


CentOS 7.0 - man page for dlasq2 (centos section 3)

Linux & Unix Commands - Search Man Pages
Man Page or Keyword Search:   man
Select Man Page Set:       apropos Keyword Search (sections above)


dlasq2.f(3)				      LAPACK				      dlasq2.f(3)

NAME
       dlasq2.f -

SYNOPSIS
   Functions/Subroutines
       subroutine dlasq2 (N, Z, INFO)
	   DLASQ2 computes all the eigenvalues of the symmetric positive definite tridiagonal
	   matrix associated with the qd Array Z to high relative accuracy. Used by sbdsqr and
	   sstegr.

Function/Subroutine Documentation
   subroutine dlasq2 (integerN, double precision, dimension( * )Z, integerINFO)
       DLASQ2 computes all the eigenvalues of the symmetric positive definite tridiagonal matrix
       associated with the qd Array Z to high relative accuracy. Used by sbdsqr and sstegr.

       Purpose:

	    DLASQ2 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 : DLASQ2 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 DLASQ3.

       Parameters:
	   N

		     N is INTEGER
		   The number of rows and columns in the matrix. N >= 0.

	   Z

		     Z is DOUBLE PRECISION 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

		     INFO is 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 100*N
			      iterations (in inner while loop).  On exit Z holds
			      a qd array with the same eigenvalues as the given Z.
			 = 3, termination criterion of outer while loop not met
			      (program created more than N unreduced blocks)

       Author:
	   Univ. of Tennessee

	   Univ. of California Berkeley

	   Univ. of Colorado Denver

	   NAG Ltd.

       Date:
	   September 2012

       Further Details:

	     Local Variables: I0:N0 defines a current unreduced segment of Z.
	     The shifts are accumulated in SIGMA. Iteration count is in ITER.
	     Ping-pong is controlled by PP (alternates between 0 and 1).

       Definition at line 113 of file dlasq2.f.

Author
       Generated automatically by Doxygen for LAPACK from the source code.

Version 3.4.2				 Tue Sep 25 2012			      dlasq2.f(3)
Unix & Linux Commands & Man Pages : ©2000 - 2018 Unix and Linux Forums


All times are GMT -4. The time now is 12:47 AM.