MB03BF

Applying iterations of a real single shifted periodic QZ algorithm to a 2-by-2 matrix product, with Hessenberg factor the last one

[Specification] [Arguments] [Method] [References] [Comments] [Example]

Purpose

  To apply at most 20 iterations of a real single shifted
  periodic QZ algorithm to the 2-by-2 product of matrices stored
  in the array A. The Hessenberg matrix is the last one of the
  formal matrix product.

Specification
      SUBROUTINE MB03BF( K, AMAP, S, SINV, A, LDA1, LDA2, ULP )
C     .. Scalar Arguments ..
      INTEGER           K, LDA1, LDA2, SINV
      DOUBLE PRECISION  ULP
C     .. Array Arguments ..
      INTEGER           AMAP(*), S(*)
      DOUBLE PRECISION  A(LDA1,LDA2,*)

Arguments

Input/Output Parameters

  K       (input)  INTEGER
          The number of factors.  K >= 1.

  AMAP    (input)  INTEGER array, dimension (K)
          The map for accessing the factors, i.e., if AMAP(I) = J,
          then the factor A_I is stored at the J-th position in A.

  S       (input)  INTEGER array, dimension (K)
          The signature array. Each entry of S must be 1 or -1.

  SINV    (input)  INTEGER
          Signature multiplier. Entries of S are virtually
          multiplied by SINV.

  A       (input/output)  DOUBLE PRECISION array, dimension
                          (LDA1,LDA2,K)
          On entry, the leading 2-by-2-by-K part of this array must
          contain a 2-by-2 product (implicitly represented by its K
          factors) in upper Hessenberg form. The Hessenberg matrix
          is the last one of the formal matrix product.
          On exit, the leading 2-by-2-by-K part of this array
          contains the product after at most 20 iterations of a real
          shifted periodic QZ algorithm.

  LDA1    INTEGER
          The first leading dimension of the array A.  LDA1 >= 2.

  LDA2    INTEGER
          The second leading dimension of the array A.  LDA2 >= 2.

  ULP     INTEGER
          The machine relation precision.

Method
  Twenty iterations of a real single shifted periodic QZ algorithm
  are applied to the 2-by-2 matrix product A.

Further Comments
  None
Example

Program Text

  None
Program Data
  None
Program Results
  None

Return to Supporting Routines index