## MB03BE

### Applying iterations of a real single shifted periodic QZ algorithm to a 2-by-2 matrix product

[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.

Specification

          SUBROUTINE MB03BE( K, AMAP, S, SINV, A, LDA1, LDA2 )
    C     .. Scalar Arguments ..
          INTEGER           K, LDA1, LDA2, SINV
    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.
              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.

Method

      Ten 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

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