Previous: tred1 Up: ../eispad.html Next: tred3

TRED2(NM,N,A,D,E,Z)

       SUBROUTINE TRED2(NM,N,A,D,E,Z)
 C
       INTEGER I,J,K,L,N,II,NM,JP1
       DOUBLE PRECISION A(NM,N),D(N),E(N),Z(NM,N)
       DOUBLE PRECISION F,G,H,HH,SCALE
 C
 C     THIS SUBROUTINE IS A TRANSLATION OF THE ALGOL PROCEDURE TRED2,
 C     NUM. MATH. 11, 181-195(1968) BY MARTIN, REINSCH, AND WILKINSON.
 C     HANDBOOK FOR AUTO. COMP., VOL.II-LINEAR ALGEBRA, 212-226(1971).
 C
 C     THIS SUBROUTINE REDUCES A REAL SYMMETRIC MATRIX TO A
 C     SYMMETRIC TRIDIAGONAL MATRIX USING AND ACCUMULATING
 C     ORTHOGONAL SIMILARITY TRANSFORMATIONS.
 C
 C     ON INPUT
 C
 C        NM MUST BE SET TO THE ROW DIMENSION OF TWO-DIMENSIONAL
 C          ARRAY PARAMETERS AS DECLARED IN THE CALLING PROGRAM
 C          DIMENSION STATEMENT.
 C
 C        N IS THE ORDER OF THE MATRIX.
 C
 C        A CONTAINS THE REAL SYMMETRIC INPUT MATRIX.  ONLY THE
 C          LOWER TRIANGLE OF THE MATRIX NEED BE SUPPLIED.
 C
 C     ON OUTPUT
 C
 C        D CONTAINS THE DIAGONAL ELEMENTS OF THE TRIDIAGONAL MATRIX.
 C
 C        E CONTAINS THE SUBDIAGONAL ELEMENTS OF THE TRIDIAGONAL
 C          MATRIX IN ITS LAST N-1 POSITIONS.  E(1) IS SET TO ZERO.
 C
 C        Z CONTAINS THE ORTHOGONAL TRANSFORMATION MATRIX
 C          PRODUCED IN THE REDUCTION.
 C
 C        A AND Z MAY COINCIDE.  IF DISTINCT, A IS UNALTERED.
 C
 C     QUESTIONS AND COMMENTS SHOULD BE DIRECTED TO BURTON S. GARBOW,
 C     MATHEMATICS AND COMPUTER SCIENCE DIV, ARGONNE NATIONAL LABORATORY
 C
 C     THIS VERSION DATED AUGUST 1983.
 C
 C     ------------------------------------------------------------------
 C